mail

MAIL(1)                    BSD General Commands Manual                   MAIL(1)

NAME
     Mail [v14.9.19] — send and receive Internet mail

SYNOPSIS
     mail [-DdEFinv~#] [-: spec] [-A account] [:-a attachment:] [:-b bcc-addr:]
          [:-C "field: body":] [:-c cc-addr:] [-M type | -m file | -q file | -t]
          [-r from-addr] [:-S var[=value]:] [-s subject] [:-T "field: addr":]
          [:-X cmd:] [:-Y cmd:] [-.] :to-addr: [-- :mta-option:]

     mail [-DdEeHiNnRv~#] [-: spec] [-A account] [:-C "field: body":] [-L spec]
          [-r from-addr] [:-S var[=value]:] [-u user] [:-X cmd:] [:-Y cmd:]
          [-- :mta-option:]
     mail [-DdEeHiNnRv~#] [-: spec] [-A account] [:-C "field: body":] -f
          [-L spec] [-r from-addr] [:-S var[=value]:] [:-X cmd:] [:-Y cmd:]
          [file] [-- :mta-option:]

     mail -h | --help
     mail -V | --version

DESCRIPTION
           Note: S-nail (Mail) will see major changes in v15.0 (circa 2020).
           Some backward incompatibilities cannot be avoided.  COMMANDS change
           to Shell-style argument quoting, and shell metacharacters will become
           (more) meaningful.  Some commands accept new syntax today via wysh
           (Command modifiers).  Behaviour is flagged [v15-compat] and [no
           v15-compat], setting v15-compat (INTERNAL VARIABLES) will choose new
           behaviour when applicable; giving it a value makes wysh an implied
           default.  [Obsolete] flags what will vanish.

           Warning! v15-compat (with value) will be a default in v14.10.0!

     Mail provides a simple and friendly environment for sending and receiving
     mail.  It is intended to provide the functionality of the POSIX mailx(1)
     command, but is MIME capable and optionally offers extensions for line
     editing, S/MIME, SMTP and POP3, among others.  Mail divides incoming mail
     into its constituent messages and allows the user to deal with them in any
     order.  It offers many COMMANDS and INTERNAL VARIABLES for manipulating
     messages and sending mail.  It provides the user simple editing
     capabilities to ease the composition of outgoing messages, and increasingly
     powerful and reliable non-interactive scripting capabilities.

   Options
     -: spec, --resource-files=..
               Explicitly control which of the Resource files shall be sourced
               (loaded): if the letter ‘s’ is (case-insensitively) part of spec
               then the system wide mail.rc is sourced, ‘u’ controls sourcing of
               the user's personal file ~/.mailrc.  The (original, unmodified)
               system resource file content is also available in the binary
               itself, and can be sourced without accessing the filesystem via
               ‘x’.  The letters ‘-’ and ‘/’ explicitly forbid sourcing of any
               resource files.  The default is ‘su’.

               Scripts should use this option: to avoid environmental noise they
               should “detach” from any configuration and create a script-
               specific environment, setting any of the desired INTERNAL
               VARIABLES via -S and running configurating commands via -X.  This
               option overrides -n.

     -A name, --account=..
               Executes an account command for the given user email account name
               after program startup is complete (all resource files are loaded,
               any -S setting is being established, but -X commands have not
               been evaluated yet).  Being a special incarnation of defined
               macros for the purpose of bundling longer-lived settings,
               activating such an email account also switches to the accounts
               primary system mailbox (most likely the inbox).  If the operation
               fails the program will exit if it is used non-interactively, or
               if any of errexit or posix are set.

     -a file[=input-charset[#output-charset]], --attach=..
               Attach file to the message (for compose mode opportunities refer
               to ~@ and ~^), after applying tilde expansion (see Filename
               transformations and folder).  Shall file not be accessible but
               contain a ‘=’ character, then anything before the last ‘=’ will
               be used as the filename, anything thereafter as a character set
               specification.

               If an input character set is specified, but no output character
               set, then the given input character set is fixed as-is, and no
               conversion will be applied; giving the empty string or the
               special string hyphen-minus ‘-’ will be treated as if ttycharset
               has been specified (the default).

               If an output character set has also been given then the
               conversion will be performed exactly as specified and on-the-fly,
               not considering the file type and content.  As an exception the
               empty string or hyphen-minus ‘-’ select the default conversion
               algorithm (see Character sets): no conversion is performed on-
               the-fly, file and its contents will be MIME-classified (HTML mail
               and MIME attachments, The mime.types files); Only this mode is
               available unless character set conversion is supported (features
               includes ‘+iconv’).

     -B        ([Obsolete]: Mail will always use line-buffered output, to gain
               line-buffered input even in batch mode enable batch mode via -#.)

     -b addr, --bcc=..
               Send a blind carbon copy to recipient addr, if the setting of
               expandaddr, one of the INTERNAL VARIABLES, allows; the ‘shquote’
               expandaddr flag is supported.  The option may be used multiple
               times.  Also see the section On sending mail, and non-interactive
               mode.

     -C "field: body", --custom-header=..
               Create a custom header which persists for an entire session.  A
               custom header consists of the field name followed by a colon ‘:’
               and the field content body, for example ‘-C "Blah: Neminem laede;
               imo omnes, quantum potes, juva"’.  Standard header field names
               cannot be overwritten by custom headers.  Runtime adjustable
               custom headers are available via the variable customhdr, and in
               compose mode ~^, one of the COMMAND ESCAPES, as well as digmsg
               are the most flexible and powerful options to manage message
               headers.  This option may be used multiple times.

     -c addr, --cc=..
               Just like -b, except it places the argument in the list of carbon
               copies.

     -D, --disconnected
               ([Option]) Startup with disconnected set.

     -d, --debug
               Enter a debug-only sandbox mode by setting the internal variable
               debug; the same can be achieved via ‘-S debug’ or ‘set debug’.
               Also see -v.

     -E, --discard-empty-messages
               set skipemptybody and thus discard messages with an empty message
               part body.

     -e, --check-and-exit
               Just check if mail is present (in the system inbox or the one
               specified via -f): if yes, return an exit status of zero, a non-
               zero value otherwise.  To restrict the set of mails to consider
               in this evaluation a message specification can be added with the
               option -L.  Quickrun: does not open an interactive session.

     -F        Save the message to send in a file named after the local part of
               the first recipient's address (instead of in record).

     -f, --file
               Read in the contents of the user's secondary mailbox MBOX (or the
               specified file) for processing; when Mail is quit, it writes
               undeleted messages back to this file (but be aware of the hold
               option).  The optional file argument will undergo some special
               Filename transformations (as via folder).  Note that file is not
               an argument to the flag -f, but is instead taken from the command
               line after option processing has been completed.  In order to use
               a file that starts with a hyphen-minus, prefix with a relative
               path, as in ‘./-hyphenbox.mbox’.

     -H, --header-summary
               Display a summary of headers for the given folder (depending on
               -u, inbox or MAIL, or as specified via -f), then exit.  A
               configurable summary view is available via the option -L.  This
               mode does not honour showlast.  Quickrun: does not open an
               interactive session.

     -h, --help
               Show a brief usage summary; use --long-help for a list long
               options.

     -i        set ignore to ignore tty interrupt signals.

     -L spec, --search=..
               Display a summary of headers of all messages that match the given
               spec in the folder found by the same algorithm used by -H, then
               exit.  See the section Specifying messages for the format of
               spec.  This mode does not honour showlast.

               If the -e option has been given in addition no header summary is
               produced, but Mail will instead indicate via its exit status
               whether spec matched any messages (‘0’) or not (‘1’); note that
               any verbose output is suppressed in this mode and must instead be
               enabled explicitly (see -v).  Quickrun: does not open an
               interactive session.

     -M type   Special send mode that will flag standard input with the MIME
               ‘Content-Type:’ set to the given known type (HTML mail and MIME
               attachments, The mime.types files) and use it as the main message
               body.  [v15 behaviour may differ] Using this option will bypass
               processing of message-inject-head and message-inject-tail.  Also
               see -q, -m, -t.

     -m file   Special send mode that will MIME classify the specified file, and
               use it as the main message body.  [v15 behaviour may differ]
               Using this option will bypass processing of message-inject-head
               and message-inject-tail.  Also see -q, -M, -t.

     -N, --no-header-summary
               inhibit the initial display of message headers when reading mail
               or editing a mailbox folder by calling unset for the internal
               variable header.

     -n        Standard flag that inhibits reading the system wide mail.rc upon
               startup.  The option -: allows more control over the startup
               sequence; also see Resource files.

     -q file, --quote-file=..
               Special send mode that will initialize the message body with the
               contents of the specified file, which may be standard input ‘-’
               only in non-interactive context.  Also see -M, -m, -t.

     -R, --read-only
               Any mailbox folder aka folder opened will be in read-only mode.

     -r from-addr, --from-address=..
               The RFC 5321 reverse-path used for relaying and delegating
               messages to its destination(s), for example to report delivery
               errors, is normally derived from the address which appears in the
               from header (or, if that contains multiple addresses, in sender).
               A file-based aka local executable mta (Mail-Transfer-Agent),
               however, instead uses the local identity of the initiating user.

               When this command line option is used the given single addressee
               from-addr will be assigned to the internal variable from, but in
               addition the command line option -f from-addr will be passed to a
               file-based mta whenever a message is sent.  Shall from-addr
               include a user name the address components will be separated and
               the name part will be passed to a file-based mta individually via
               -F name.  Even though not a recipient the ‘shquote’ expandaddr
               flag is supported.

               If an empty string is passed as from-addr then the content of the
               variable from (or, if that contains multiple addresses, sender)
               will be evaluated and used for this purpose whenever the file-
               based mta is contacted.  By default, without -r that is, neither
               -f nor -F command line options are used when contacting a file-
               based MTA, unless this automatic deduction is enforced by seting
               the internal variable r-option-implicit.

               Remarks: many default installations and sites disallow overriding
               the local user identity like this unless either the MTA has been
               configured accordingly or the user is member of a group with
               special privileges.  Passing an invalid address will cause an
               error.

     -S var[=value], --set=..
               set (or, with a prefix string ‘no’, as documented in INTERNAL
               VARIABLES, unset) variable and optionally assign value, if
               supported; [v15 behaviour may differ] the entire expression is
               evaluated as if specified within dollar-single-quotes (see
               Shell-style argument quoting) if the internal variable v15-compat
               is set.  If the operation fails the program will exit if any of
               errexit or posix are set.  Settings established via -S cannot be
               changed from within Resource files or an account switch initiated
               by -A.  They will become mutable again before commands registered
               via -X are executed.

     -s subject, --subject=..
               Specify the subject of the message to be sent.  Newline (NL) and
               carriage-return (CR) bytes are invalid and will be normalized to
               space (SP) characters.

     -T "field: addr", --target=..
               Add addr to the list of receivers targeted by field, for now
               supported are only ‘bcc’, ‘cc’, ‘fcc’, and ‘to’.  Field and body
               (address) are separated by a colon ‘:’ and optionally blank
               (space, tabulator) characters.  The ‘shquote’ expandaddr flag is
               supported.  addr is parsed like a message header address line, as
               if it would be part of a template message fed in via -t, and the
               same modifier suffix is supported.  This option may be used
               multiple times.

     -t, --template
               The text message given (on standard input) is expected to
               contain, separated from the message body by an empty line, one or
               multiple plain text message headers.  [v15 behaviour may differ]
               Readily prepared MIME mail messages cannot be passed.  Headers
               can span multiple consecutive lines if follow lines start with
               any amount of whitespace.  A line starting with the number sign
               ‘#’ in the first column is ignored.  Message recipients can be
               given via the message headers ‘To:’, ‘Cc:’, ‘Bcc:’ (the ‘?single’
               modifier enforces treatment as a single addressee, for example
               ‘To?single: exa, <m@ple>’) or ‘Fcc:’, they will be added to any
               recipients specified on the command line, and are likewise
               subject to expandaddr validity checks.  If a message subject is
               specified via ‘Subject:’ then it will be used in favour of one
               given on the command line.

               More optional headers are ‘Reply-To:’ (possibly overriding
               reply-to), ‘Sender:’ (sender), ‘From:’ (from and / or option -r).
               ‘Message-ID:’, ‘In-Reply-To:’, ‘References:’ and
               ‘Mail-Followup-To:’, by default created automatically dependent
               on message context, will be used if specified (a special address
               massage will however still occur for the latter).  Any other
               custom header field (also see -C, customhdr and ~^) is passed
               through entirely unchanged, and in conjunction with the options
               -~ or -# it is possible to embed COMMAND ESCAPES.  Also see -M,
               -m, -q.

     -u user, --inbox-of=..
               Initially read the primary system mailbox of user, appropriate
               privileges presumed; effectively identical to ‘-f %user’.

     -V, --version
               Show Mails version and exit.  The command version will also show
               the list of features: ‘$ mail -:/ -Xversion -Xx’.

     -v, --verbose
               sets the internal variable verbose to enable logging of
               informational context messages.  (Increases level of verbosity
               when used multiple times.)  Also see -d.

     -X cmd, --startup-cmd=..
               Add the given (or multiple for a multiline argument) cmd to a
               list of commands to be executed before normal operation starts.
               The commands will be evaluated as a unit, just as via source.
               Correlates with -# and errexit.

     -Y cmd, --cmd=..
               Add the given (or multiple for a multiline argument) cmd to a
               list of commands to be executed after normal operation has
               started.  The commands will be evaluated successively in the
               given order, and as if given on the program's standard input —
               before interactive prompting begins in interactive mode, after
               standard input has been consumed otherwise.

     -~, --enable-cmd-escapes
               Enable COMMAND ESCAPES in compose mode even in non-interactive
               use cases.  This can for example be used to automatically format
               the composed message text before sending the message:

                     $ ( echo 'line    one. Word.     Word2.';\
                         echo '~| /usr/bin/fmt -tuw66' ) |\
                       LC_ALL=C mail -d~:/ -Sttycharset=utf-8 bob@exam.ple

     -#, --batch-mode
               Enables batch mode: standard input is made line buffered, the
               complete set of (interactive) commands is available, processing
               of COMMAND ESCAPES is enabled in compose mode, and diverse
               INTERNAL VARIABLES are adjusted for batch necessities, exactly as
               if done via -S: emptystart, noerrexit, noheader, noposix, quiet,
               sendwait, typescript-mode as well as MAIL, MBOX and inbox (the
               latter three to /dev/null).  Also, the values of COLUMNS and
               LINES are looked up, and acted upon.  The following prepares an
               email message in a batched dry run:

                     $ LC_ALL=C printf 'm bob\n~s ubject\nText\n~.\nx\n' |\
                       LC_ALL=C mail -d#:x -X'alias bob bob@exam.ple'

     -., --end-options
               This flag forces termination of option processing in order to
               prevent “option injection” (attacks).  It also forcefully puts
               Mail into send mode, see On sending mail, and non-interactive
               mode.

     All given to-addr arguments and all receivers established via -b and -c as
     well as -T are subject to the checks established by expandaddr, one of the
     INTERNAL VARIABLES; they all support the flag ‘shquote’.  If the setting of
     expandargv allows their recognition all mta-option arguments given at the
     end of the command line after a ‘--’ separator will be passed through to a
     file-based mta (Mail-Transfer-Agent) and persist for the entire session.
     expandargv constraints do not apply to the content of mta-arguments.

   A starter
     Mail is a direct descendant of BSD Mail, itself a successor to the Research
     UNIX mail which “was there from the start” according to HISTORY.  It thus
     represents the user side of the UNIX mail system, whereas the system side
     (Mail-Transfer-Agent, MTA) was traditionally taken by sendmail(8) (and most
     MTAs provide a binary of this name for compatibility reasons).  If the
     [Option]al SMTP mta is included in the features of Mail then the system
     side is not a mandatory precondition for mail delivery.

     Mail strives for compliance with the POSIX mailx(1) standard, but posix,
     one of the INTERNAL VARIABLES (or its ENVIRONMENTal equivalent
     POSIXLY_CORRECT), needs to be set to adjust behaviour to be almost on par.
     Almost, because there is one important difference: POSIX Shell-style
     argument quoting is ([v15 behaviour may differ] increasingly) used instead
     of the Old-style argument quoting that the standard documents, which is
     believed to be a feature.  The builtin as well as the (default) global
     mail.rc Resource files already bend the standard imposed settings a bit.

     For example, hold and keepsave are set in order to suppress the automatic
     moving of messages to the secondary mailbox MBOX that would otherwise occur
     (see Message states), and keep to not remove empty system MBOX mailbox
     files (or all empty such files in posix mode) to avoid mangling of file
     permissions when files eventually get recreated.

     To enter interactive mode even if the initial mailbox is empty emptystart
     is set, editheaders to allow editing of headers as well as fullnames to not
     strip down addresses in compose mode, and quote to include the message that
     is being responded to when replying, which is indented by an indentprefix
     that also deviates from standard imposed settings.  mime-counter-evidence
     is fully enabled, too.  It sets followup-to-honour and reply-to-honour to
     comply with reply address desires.

     Random remarks.  The file mode creation mask can be managed explicitly via
     the variable umask.  Files and shell pipe output can be sourced for
     evaluation, also during startup from within the Resource files.
     Informational context can be available by setting verbose or debug (as via
     -v, -d).

   On sending mail, and non-interactive mode
     To send a message to one or more people, using a local or built-in mta
     (Mail-Transfer-Agent) transport to actually deliver the generated mail
     message, Mail can be invoked with arguments which are the names of people
     to whom the mail will be sent, and the command line options -b and -c can
     be used to add (blind) carbon copy receivers:

           # Via test MTA
           $ echo Hello, world | mail -:/ -Smta=test -s test $LOGNAME

           # Via sendmail(1) MTA
           $ </dev/null mail -:x -s test $LOGNAME

           # Debug dry-run mode:
           $ </dev/null LC_ALL=C mail -d -:/ \
              -Sttycharset=utf8 -Sfullnames \
              -b bcc@exam.ple -c cc@exam.ple -. \
              '(Lovely) Bob <bob@exam.ple>' eric@exam.ple

           # With SMTP (no real sending due to -d debug dry-run)
           $ LC_ALL=C mail -d -:/ -Sv15-compat -Sttycharset=utf8 \
               -S mta=smtps://mylogin@exam.ple:465 -Ssmtp-auth=none \
               -S from=scriptreply@exam.ple \
               -a /etc/mail.rc --end-options \
               eric@exam.ple < /tmp/letter.txt

     If standard input is a terminal rather than the message to be sent, the
     user is expected to type in the message contents.  In this compose mode
     Mail treats lines beginning with the character ‘~’ special – these are so-
     called COMMAND ESCAPES, which can be used to read in files, process shell
     commands, add and edit attachments and more; for example ~v or ~e will
     start the VISUAL text EDITOR, respectively, to revise the message in its
     current state, ~h allows editing of the most important message headers,
     with the potent ~^ custom headers can be created, for example (more
     specifically than with -C and customhdr).  [Option]ally ~? gives an
     overview of most other available command escapes.

     The command escape ~. (see there) will call hooks, insert automatic
     injections and receivers, leave compose mode and send the message once it
     is completed.  Aborting letter composition is possible with either of ~x or
     ~q, the latter of which will save the message in the file denoted by DEAD
     unless nosave is set.  And unless ignoreeof is set the effect of ~. can
     also be achieved by typing end-of-transmission (EOT) via ‘control-D’ (‘^D’)
     at the beginning of an empty line, and ~q is always reachable by typing
     end-of-text (ETX) twice via ‘control-C’ (‘^C’).

     A number of ENVIRONMENT and INTERNAL VARIABLES can be used to alter default
     behavior.  setting (also via -S) editalong will automatically startup an
     editor when compose mode is entered, and editing of headers additionally to
     plain body content can be enabled via editheaders: [v15 behaviour may
     differ] some, but not all headers can be created, edited or deleted in an
     editor, then.  askcc and askbcc will cause the user to be prompted actively
     for (blind) carbon-copy recipients, respectively, and (the default) asksend
     will request confirmation whether the message shall be sent.

     The envelope sender address is defined by from, explicitly defining an
     originating hostname may be desirable, especially with the built-in SMTP
     Mail-Transfer-Agent mta.  Character sets for outgoing message and MIME part
     content are configurable via sendcharsets, whereas input data is assumed to
     be in ttycharset.  Message data will be passed over the wire in a
     mime-encoding.  MIME parts aka attachments need to be assigned a mimetype,
     usually taken out of The mime.types files.  Saving a copy of sent messages
     in a record mailbox may be desirable – as for most mailbox folder targets
     the value will undergo Filename transformations.  Some introductional -d or
     debug sandbox dry-run tests will prove correctness.

     Message recipients are subject to alternates filtering, and may not only be
     email addresses, but can also be names of mailboxes and even complete shell
     command pipe specifications.  If the variable expandaddr is not set then
     only email addresses like ‘bob@exam.ple’ and plain user names (including
     MTA aliases) may be used, other types will be filtered out, giving a
     warning message.  expandaddr indeed allows further control over and
     adjustments of message recipients, for example user names can be expanded
     to network addresses by specifying ‘nametoaddr’.  A network address that
     contains no domain-, but only a valid local user ‘<name>’ in angle brackets
     will be automatically expanded to a valid address when hostname is not set,
     or set to a non-empty value; setting it to the empty value instructs Mail
     that the used mta will perform the necessary expansion.  The command
     addrcodec may help to generate standard compliant network addresses.

     If the variable expandaddr is set then an extended set of recipient
     addresses will be accepted: Any name that starts with a vertical bar ‘|’
     character specifies a command pipe – the command string following the ‘|’
     is executed and the message is sent to its standard input; Likewise, any
     name that consists only of hyphen-minus ‘-’ or starts with the character
     solidus ‘/’ or the character sequence dot solidus ‘./’ is treated as a
     file, regardless of the remaining content.  Any other name which contains a
     commercial at ‘@’ character is a network address; Any other name which
     starts with a plus sign ‘+’ character is a mailbox name; Any other name
     which contains a solidus ‘/’ character but no exclamation mark ‘!’ or
     percent sign ‘%’ character before is also a mailbox name; What remains is
     treated as a network address.

           $ echo bla | mail -Sexpandaddr -s test ./mbox.mbox
           $ echo bla | mail -Sexpandaddr -s test '|cat >> ./mbox.mbox'
           $ echo safe | LC_ALL=C \
               mail -:/ -Sv15-compat -Sttycharset=utf8 \
                 --set mime-force-sendout \
                 -Sexpandaddr=fail,-all,+addr,failinvaddr -s test \
                 --end-options bob@exam.ple

     To create file-carbon-copies the special recipient header ‘Fcc:’ may be
     used as often as desired.  Its entire value (or body in standard terms) is
     interpreted as a folder target, after having been subject to Filename
     transformations.  Beside using the command escape ~^ (to create a ‘Fcc’
     header) this is the only way to create a file-carbon-copy without
     introducing an ambiguity regarding the interpretation of the address, file
     names with leading vertical bars or commercial ats can be used.  Like all
     other recipients ‘Fcc:’ is subject to the checks of expandaddr.  Any local
     file and pipe command addressee honours the setting of mbox-fcc-and-pcc.

     It is possible to create personal distribution lists via the alias command,
     so that, for instance, the user can send mail to ‘cohorts’ and have it go
     to a group of people.  Different to the alias mechanism of most local mtas,
     often documented in aliases(5) and subject to the ‘name’ constraint of
     expandaddr, personal aliases will be expanded by Mail before the message is
     sent.  They are thus a convenient alternative to specifying each addressee
     by itself, correlate with the active set of alternates, and are subject to
     metoo filtering.  [Option]ally MTA aliases can be expanded before sending
     messages by setting mta-aliases.

           ? alias  cohorts  bill jkf mark kridle@ucbcory ~/cohorts.mbox
           ? alias  mark  mark@exam.ple
           ? set mta-aliases=/etc/aliases

     For the purpose of arranging a complete environment of settings that can be
     switched to with a single command or command line option there are
     accounts.  Alternatively it is also possible to use a flat configuration,
     making use of so-called variable chains which automatically pick
     ‘USER@HOST’ or ‘HOST’ context-dependent variable variants: for example
     addressing ‘Folder pop3://yaa@exam.ple’ would find
     pop3-no-apop-yaa@exam.ple, pop3-no-apop-exam.ple and pop3-no-apop in order.
     See On URL syntax and credential lookup and INTERNAL VARIABLES.

     The compose mode hooks on-compose-enter, on-compose-splice,
     on-compose-leave and on-compose-cleanup may be set to defined macros and
     provide reliable and increasingly powerful mechanisms to perform automated
     message adjustments dependent on message context, for example addition of
     message signatures (message-inject-head, message-inject-tail) or creation
     of additional receiver lists (also by setting autocc, autobcc).  To achieve
     that the command digmsg may be used in order to query and adjust status of
     message(s).  The splice hook can also make use of COMMAND ESCAPES.  ([v15
     behaviour may differ] The compose mode hooks work for forward, mail, reply
     and variants; resend and Resend only provide the hooks on-resend-enter and
     on-resend-cleanup, which are pretty restricted due to the nature of the
     operation.)

     To avoid environmental noise scripts should “detach” Mail from any
     configuration files and create a script-local environment, ideally with the
     command line options -: to disable any configuration file in conjunction
     with repetitions of -S to specify variables:

           $ env LC_ALL=C mail -:/ \
               -Sv15-compat \
               -Sttycharset=utf-8 -Smime-force-sendout \
               -Sexpandaddr=fail,-all,failinvaddr \
               -S mta=smtps://mylogin@exam.ple:465 -Ssmtp-auth=login \
               -S from=scriptreply@exam.ple \
               -s 'Subject to go' -a attachment_file \
               -Sfullnames -. \
               'Recipient 1 <rec1@exam.ple>' rec2@exam.ple \
               < content_file

     As shown, scripts can “fake” a locale environment, the above specifies the
     all-compatible 7-bit clean LC_ALL “C”, but will nonetheless take and send
     UTF-8 in the message text by using ttycharset.  If character set conversion
     is compiled in (features includes the term ‘+iconv’) invalid (according to
     ttycharset) character input data would normally cause errors; setting
     mime-force-sendout will instead, as a last resort, classify the input as
     binary data, and therefore allow message creation to be successful.  (Such
     content can then be inspected either by installing a pipe-TYPE/SUBTYPE
     handler for ‘application/octet-stream’, or possibly automatically through
     mime-counter-evidence).

     In interactive mode, which is introduced in the next section, messages can
     be sent by calling the mail command with a list of recipient addresses:

           $ mail -d -Squiet -Semptystart
           "/var/spool/mail/user": 0 messages
           ? mail "Recipient 1 <rec1@exam.ple>", rec2@exam.ple
           ...
           ? # Will do the right thing (tm)
           ? m rec1@exam.ple rec2@exam.ple

   On reading mail, and interactive mode
     When invoked without addressees Mail enters interactive mode in which mails
     may be read.  When used like that the user's system inbox (for more on
     mailbox types please see the command folder) is read in and a one line
     header of each message therein is displayed if the variable header is set.
     The visual style of this summary of headers can be adjusted through the
     variable headline and the possible sorting criterion via autosort.
     Scrolling through screenfuls of headers can be performed with the command
     z.  If the initially opened mailbox is empty Mail will instead exit
     immediately (after displaying a message) unless the variable emptystart is
     set.

     At the prompt the command list will give a listing of all available
     commands and help will [Option]ally give a summary of some common ones.  If
     the [Option]al documentation strings are available (see features) one can
     type ‘help X’ (or ‘?X’) and see the actual expansion of ‘X’ and what its
     purpose is, i.e., commands can be abbreviated (note that POSIX defines some
     abbreviations, so that the alphabetical order of commands does not
     necessarily relate to the abbreviations; it is however possible to define
     overwrites with commandalias).  These commands can also produce a more
     verbose output.

     Messages are given numbers (starting at 1) which uniquely identify
     messages; the current message – the “dot” – will either be the first new
     message, or the first unread message, or the first message of the mailbox;
     the internal variable showlast will instead cause usage of the last message
     for this purpose.  The command headers will display a screenful of header
     summaries containing the “dot”, whereas from will display only the
     summaries of the given messages, defaulting to the “dot”.

     Message content can be displayed with the command type (‘t’, alias print).
     Here the variable crt controls whether and when Mail will use the
     configured PAGER for display instead of directly writing to the user
     terminal screen, the sole difference to the command more, which will always
     use the PAGER.  The command top will instead only show the first toplines
     of a message (maybe even compressed if topsqueeze is set).  Message display
     experience may improve by setting and adjusting mime-counter-evidence, and
     also see HTML mail and MIME attachments.

     By default the current message (“dot”) is displayed, but like with many
     other commands it is possible to give a fancy message specification (see
     Specifying messages), for example ‘t:u’ will display all unread messages,
     ‘t.’ will display the “dot”, ‘t 1 5’ will type the messages 1 and 5, ‘t
     1-5’ will type the messages 1 through 5, and ‘t-’ and ‘t+’ will display the
     previous and the next message, respectively.  The command search (a more
     substantial alias for from) will display a header summary of the given
     message specification list instead of their content; the following will
     search for subjects:

           ? from '@Some subject to search for'

     In the default setup all header fields of a message will be typed, but
     fields can be white- or blacklisted for a variety of applications by using
     the command headerpick, e.g., to restrict their display to a very
     restricted set for type: ‘headerpick type retain from to cc subject’.  In
     order to display all header fields of a message regardless of currently
     active ignore or retain lists, use the commands Type and Top; Show will
     show the raw message content.  Note that historically the global mail.rc
     not only adjusts the list of displayed headers, but also sets crt.  ([v15
     behaviour may differ] A yet somewhat restricted) Reliable scriptable
     message inspection is available via digmsg.

     Dependent upon the configuration a line editor (see the section On terminal
     control and line editor) aims at making the user experience with the many
     COMMANDS a bit nicer.  When reading the system inbox, or when -f (or
     folder) specified a mailbox explicitly prefixed with the special ‘%:’
     modifier (to propagate it to a primary system mailbox), then messages which
     have been read (see Message states) will be automatically moved to a
     secondary mailbox, the user's MBOX file, when the mailbox is left, either
     by changing the active mailbox or by quitting Mail – this automatic moving
     from a system- or primary- to the secondary mailbox is not performed when
     the variable hold is set.  Messages can also be explicitly moved to other
     mailboxes, whereas copy keeps the original message.  write can be used to
     write out data content of specific parts of messages.

     After examining a message the user can reply ‘r’ to the sender and all
     recipients (which will also be placed in ‘To:’ unless recipients-in-cc is
     set), or Reply ‘R’ exclusively to the sender(s).  To comply with with the
     receivers desired reply address the quadoptions followup-to-honour and
     reply-to-honour should usually be set.  The commands Lreply and Lfollowup
     know how to apply a special addressee massage, see Mailing lists.
     Dependent on the presence and value of quote the message being replied to
     will be included in a quoted form.  forwarding a message will allow editing
     the new message: the original message will be contained in the message
     body, adjusted according to headerpick.  It is possible to resend or Resend
     messages: the former will add a series of ‘Resent-’ headers, whereas the
     latter will not; different to newly created messages editing is not
     possible and no copy will be saved even with record unless the additional
     variable record-resent is set.  When sending, replying or forwarding
     messages comments and full names will be stripped from recipient addresses
     unless the internal variable fullnames is set.

     Of course messages can be delete ‘d’, and they can spring into existence
     again via undelete, or when the Mail session is ended via the exit or xit
     commands to perform a quick program termation.  To end a mail processing
     session regulary and perform a full program exit one may issue the command
     quit.  It will, among others, move read messages to the secondary mailbox
     MBOX as necessary, discard deleted messages in the current mailbox, and
     update the [Option]al (see features) line editor history-file.  By the way,
     whenever the main event loop is about to look out for the next input line
     it will trigger the hook on-main-loop-tick.

   HTML mail and MIME attachments
     HTML-only messages become more and more common, and many messages come
     bundled with a bouquet of MIME (Multipurpose Internet Mail Extensions)
     parts and attachments.  To get a notion of MIME types Mail has a default
     set of types built-in, onto which the content of The mime.types files will
     be added (as configured and allowed by mimetypes-load-control).  Types can
     also become registered with the command mimetype.  To improve interaction
     with the faulty MIME part declarations of real life mime-counter-evidence
     will allow verification of the given assertion, and the possible provision
     of an alternative, better MIME type.

     Whereas a simple HTML-to-text filter for displaying HTML messages is
     [Option]ally supported (indicated by ‘+filter-html-tagsoup’ in features),
     MIME types other than plain text cannot be handled directly.  Instead
     programs need to become registered to deal with specific MIME types or file
     extensions, either to prepare (re-)integrable plain text versions of their
     input (a mode which is called copiousoutput), or to display the content
     externally, for example in a graphical window: the latter type is only
     considered by and for the command mimeview.

     To install a handler program for a MIME type an according pipe-TYPE/SUBTYPE
     variable needs to be set; to define a handler for a file extension
     pipe-EXTENSION can be used – these handlers take precedence.  [Option]ally
     mail user agent configuration is supported (see The Mailcap files), and
     will be queried for display or quote handlers after the former ones.  Type-
     markers registered via mimetype are the last possible source for
     information how to handle a MIME type.

     For example, to display HTML messages integrated via the text browsers
     lynx(1) or elinks(1), register a MathML MIME type and enable its plain text
     display, and to open PDF attachments in an external PDF viewer,
     asynchronously and with some other magic attached:

           ? if "$features" !% +filter-html-tagsoup
           ?   #set pipe-text/html='?* elinks -force-html -dump 1'
           ?   set pipe-text/html='?* lynx -stdin -dump -force_html'
           ?   # Display HTML as plain text instead
           ?   #set pipe-text/html=?t
           ? endif
           ? mimetype ?t application/mathml+xml mathml
           ? wysh set pipe-application/pdf='?&=? \
               trap "rm -f \"${MAILX_FILENAME_TEMPORARY}\"" EXIT;\
               trap "trap \"\" INT QUIT TERM; exit 1" INT QUIT TERM;\
               mupdf "${MAILX_FILENAME_TEMPORARY}"'

   Mailing lists
     Known or subscribed-to mailing lists may be flagged in the summary of
     headers (headline format character ‘%L’), and will gain special treatment
     when sending mails: the variable followup-to-honour will ensure that a
     ‘Mail-Followup-To:’ header is honoured when a message is being replied to
     (reply, followup, Lreply, Lfollowup), and followup-to controls creation of
     this header when creating mails, if the necessary user setup (from,
     sender); is available; then, it may also be created automatically, for
     example when list-replying via Lreply or Lfollowup, when followup or reply
     is used and the messages ‘Mail-Followup-To:’ is honoured etc.

     The commands mlist and mlsubscribe manage Mails notion of which addresses
     are mailing lists.  With the [Option]al regular expression support any
     address which contains any of the magic regular expression characters
     (‘^[*+?|$’; see re_format(7) or regex(7), dependent on the host system)
     will be compiled and used as one, possibly matching many addresses.  It is
     not possible to escape the “magic”: in order to match special characters
     as-is, bracket expressions must be used, for example ‘search
     @subject@'[[]open bracket'’.

           ? set followup-to followup-to-honour=ask-yes \
               reply-to-honour=ask-yes
           ? mlist a1@b1.c1 a2@b2.c2 '.*@lists\.c3$'
           ? mlsubscribe a4@b4.c4 exact@lists.c3

     Known and subscribed lists differ in that for the latter the users address
     is not part of a generated ‘Mail-Followup-To:’.  There are exceptions, for
     example if multiple lists are addressed and not all have the subscription
     attribute.  When replying to a message its list address (‘List-Post:’
     header) is automatically and temporarily treated like a known mlist;
     dependent on the variable reply-to-honour an existing ‘Reply-To:’ is used
     instead (if it is a single address on the same domain as ‘List-Post:’) in
     order to accept a list administrator's wish that is supposed to have been
     manifested like that.

     For convenience and compatibility with mail programs that do not honour the
     non-standard M-F-T, an automatic user entry in the carbon-copy ‘Cc:’
     address list of generated message can be created by setting
     followup-to-add-cc.  This entry will be added whenever the user will be
     placed in the ‘Mail-Followup-To:’ list, and is not a regular addressee
     already.  reply-to-swap-in tries to deal with the address rewriting that
     many mailing-lists nowadays perform to work around DKIM / DMARC etc.
     standard imposed problems.

   Signed and encrypted messages with S/MIME
     [Option] S/MIME provides two central mechanisms: message signing and
     message encryption.  A signed message contains some data in addition to the
     regular text.  The data can be used to verify that the message has been
     sent using a valid certificate, that the sender address matches that in the
     certificate, and that the message text has not been altered.  Signing a
     message does not change its regular text; it can be read regardless of
     whether the recipients software is able to handle S/MIME.  It is thus
     usually possible to sign all outgoing messages if so desired.

     Encryption, in contrast, makes the message text invisible for all people
     except those who have access to the secret decryption key.  To encrypt a
     message, the specific recipients public encryption key must be known.  It
     is therefore not possible to send encrypted mail to people unless their key
     has been retrieved from either previous communication or public key
     directories.  Because signing is performed with private keys, and
     encryption with public keys, messages should always be signed before being
     encrypted.

     A central concept to S/MIME is that of the certification authority (CA).  A
     CA is a trusted institution that issues certificates.  For each of these
     certificates it can be verified that it really originates from the CA,
     provided that the CA's own certificate is previously known.  A set of CA
     certificates is usually delivered and installed together with the
     cryptographical library that is used on the local system.  Therefore
     reasonable security for S/MIME on the Internet is provided if the source
     that provides that library installation is trusted.  It is also possible to
     use a specific pool of trusted certificates.  If this is desired,
     smime-ca-no-defaults should be set to avoid using the default certificate
     pool, and smime-ca-file and/or smime-ca-dir should be pointed to a trusted
     pool of certificates.  A certificate cannot be more secure than the method
     its CA certificate has been retrieved with.

     This trusted pool of certificates is used by the command verify to ensure
     that the given S/MIME messages can be trusted.  If so, verified sender
     certificates that were embedded in signed messages can be saved locally
     with the command certsave, and used by Mail to encrypt further
     communication with these senders:

           ? certsave FILENAME
           ? set smime-encrypt-USER@HOST=FILENAME \
               smime-cipher-USER@HOST=AES256

     To sign outgoing messages, in order to allow receivers to verify the origin
     of these messages, a personal S/MIME certificate is required.  Mail
     supports password-protected personal certificates (and keys), see
     smime-sign-cert.  The section On URL syntax and credential lookup gives an
     overview of the possible sources of user credentials, and S/MIME step by
     step shows examplarily how a private S/MIME certificate can be obtained.
     In general, if such a private key plus certificate “pair” is available, all
     that needs to be done is to set some variables:

           ? set smime-sign-cert=ME@exam.ple.paired \
               smime-sign-digest=SHA512 \
               smime-sign from=myname@my.host

     Variables of interest for S/MIME in general are smime-ca-dir,
     smime-ca-file, smime-ca-flags, smime-ca-no-defaults, smime-crl-dir,
     smime-crl-file.  For S/MIME signing of interest are smime-sign,
     smime-sign-cert, smime-sign-include-certs and smime-sign-digest.
     Additional variables of interest for S/MIME en- and decryption:
     smime-cipher and smime-encrypt-USER@HOST.  Variables of secondary interest
     may be content-description-smime-message and
     content-description-smime-signature.  S/MIME is available if ‘+smime’ is
     included in features.

     [v15 behaviour may differ] Note that neither S/MIME signing nor encryption
     applies to message subjects or other header fields yet.  Thus they may not
     contain sensitive information for encrypted messages, and cannot be trusted
     even if the message content has been verified.  When sending signed
     messages, it is recommended to repeat any important header information in
     the message text.

   On URL syntax and credential lookup
     For accessing protocol-specific resources Uniform Resource Locators (URL,
     RFC 3986) have become omnipresent.  Here they are expected in a
     “normalized” variant, not used in data exchange, but only meant as a
     compact, easy-to-use way of defining and representing information in a
     well-known notation; as such they do not conform to any real standard.
     Optional parts are placed in brackets ‘[]’, optional either because there
     also exist other ways to define the information, or because the part is
     protocol specific.  ‘/path’ for example is used by the [Option]al Maildir
     folder type and the IMAP protocol, but not by POP3.  If ‘USER’ and
     ‘PASSWORD’ are included in an URL server specification, URL percent encoded
     (RFC 3986) forms are needed, generable with urlcodec.

           PROTOCOL://[USER[:PASSWORD]@]server[:port][/path]

     Often INTERNAL VARIABLES exist in multiple versions, called “variable
     chains” in this document: the plain ‘variable’ as well as ‘variable-HOST’
     and ‘variable-USER@HOST’.  If a port was specified ‘HOST’ really means
     ‘server:port’, not ‘server’.  And this ‘USER’ is never in URL percent
     encoded form.  For example, whether the hypothetical ‘smtp://wings%3Aof
     @a.dove’ including user and password was used, or whether it was
     ‘smtp://a.dove’ and it came from a different source, to lookup the chain
     tls-config-pairs first ‘tls-config-pairs-wings:of@a.dove’ is looked up,
     then ‘tls-config-pairs-a.dove’, before finally looking up the plain
     variable.

     The logic to collect (an accounts) credential information is as follows:

     A user is always required.  If no ‘USER’ has been given in the URL the
         variables user-HOST and user are looked up.  Afterwards, when enforced
         by the [Option]al variables netrc-lookup-HOST or netrc-lookup, The
         .netrc file of the user will be searched for a ‘HOST’ specific entry
         which provides a ‘login’ name: only unambiguous entries are used (one
         possible matching entry for ‘HOST’).

         If there is still no ‘USER’ then the verified LOGNAME, known to be a
         valid user on the current host, is used.

     Authentication: unless otherwise noted the chain
         PROTOCOL-auth-USER@HOST, PROTOCOL-auth-HOST, PROTOCOL-auth is checked,
         falling back to a protocol-specific default as necessary.

     If no ‘PASSWORD’ has been given in the URL, then if the ‘USER’ has been
         found through the [Option]al netrc-lookup, that may have also provided
         the password.  Otherwise the chain password-USER@HOST, password-HOST,
         password is looked up.

         Thereafter the (now complete) [Option]al chain netrc-lookup-USER@HOST,
         netrc-lookup-HOST, netrc-lookup is checked, if set the netrc cache is
         searched for a password only (multiple user accounts for a single
         machine may exist as well as a fallback entry without user but with a
         password).

         If at that point there is still no password available, but the
         (protocols') chosen authentication type requires a password, then in
         interactive mode the user will be prompted on the terminal.

     Note: S/MIME verification works relative to the values found in the ‘From:’
     (or ‘Sender:’) header field(s), which means the values of smime-sign,
     smime-sign-cert, smime-sign-include-certs and smime-sign-digest will not be
     looked up using the ‘USER’ and ‘HOST’ chains from above, but instead use
     the corresponding values from the message that is being worked on.  If no
     address matches we assume and use the setting of from.  In unusual cases
     multiple and different ‘USER’ and ‘HOST’ combinations may therefore be
     involved – on the other hand those unusual cases become possible.  The
     usual case is as short as:

           set mta=smtp://USER:PASS@HOST smtp-use-starttls \
               smime-sign smime-sign-cert=+smime.pair \
               from=myname@my.host

     The section EXAMPLES contains complete example configurations.

   Encrypted network communication
     [Option] SSL (Secure Sockets Layer) aka its successor TLS (Transport Layer
     Security) are protocols which aid in securing communication by providing a
     safely initiated and encrypted network connection.  A central concept of
     TLS are certificates: as part of each network connection setup a (set of)
     certificates will be exchanged through which the identity of the network
     peer can be cryptographically verified; if possible the TLS/SNI
     (ServerNameIndication) extension will be enabled to allow servers fine-
     grained control over the certificates being used.  A locally installed pool
     of trusted certificates will then be inspected, and verification will
     succeed if it contains a(n in)direct signer of the presented
     certificate(s).

     The local pool of trusted so-called CA (Certification Authority)
     certificates is usually delivered with and used along the TLS library.  A
     custom pool of trusted certificates can be selected by pointing tls-ca-file
     and/or (with special preparation) tls-ca-dir to the desired location;
     setting tls-ca-no-defaults in addition will avoid additional inspection of
     the default pool.  A certificate cannot be more secure than the method its
     CA certificate has been retrieved with.  For inspection or other purposes,
     the certificate of a server (as seen when connecting to it) can be fetched
     with the command tls (port can usually be the protocol name, too, and
     tls-verify is taken into account here):

           $ mail -vX 'tls certchain SERVER-URL[:PORT]; x'

     A local pool of CA certificates is not strictly necessary, however, server
     certificates can also be verified via their fingerprint.  For this a
     message digest will be calculated and compared against the variable chain
     tls-fingerprint, and verification will succeed if the fingerprint matches.
     The message digest (algorithm) can be configured via the variable chain
     tls-fingerprint-digest; tls can again be used:

           $ mail -X 'wysh set verbose; tls fingerprint SERVER-URL[:PORT]; x'

     It depends on the used protocol whether encrypted communication is
     possible, and which configuration steps have to be taken to enable it.
     Some protocols, like POP3S, are implicitly encrypted, others, like POP3,
     can upgrade a plain text connection if so requested.  For example, to use
     the ‘STLS’ that POP3 offers (a member of) the variable (chain)
     pop3-use-starttls needs to be set, with convenience via shortcut:

           shortcut encpop1 pop3s://pop1.exam.ple

           shortcut encpop2 pop3://pop2.exam.ple
           set pop3-use-starttls-pop2.exam.ple

           set mta=smtps://smtp.exam.ple:465
           set mta=smtp://smtp.exam.ple smtp-use-starttls

     Normally that is all there is to do, given that TLS libraries try to
     provide safe defaults, plenty of knobs however exist to adjust settings.
     For example certificate verification settings can be fine-tuned via
     tls-ca-flags, and the TLS configuration basics are accessible via
     tls-config-pairs, for example to control protocol versions or cipher lists.
     In the past hints on how to restrict the set of protocols to highly secure
     ones were indicated, but as of the time of this writing the list of
     protocols or ciphers may need to become relaxed in order to be able to
     connect to some servers; the following example allows connecting to a
     “Lion” that uses OpenSSL 0.9.8za from June 2014 (refer to INTERNAL
     VARIABLES for more on variable chains):

           wysh set tls-config-pairs-lion@exam.ple='MinProtocol=TLSv1.1,\
               CipherString=TLSv1.2:!aNULL:!eNULL:\
                 ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:\
                 DHE-RSA-AES256-SHA:@STRENGTH'

     The OpenSSL program ciphers(1) should be referred to when creating a custom
     cipher list.  Variables of interest for TLS in general are tls-ca-dir,
     tls-ca-file, tls-ca-flags, tls-ca-no-defaults, tls-config-file,
     tls-config-module, tls-config-pairs, tls-crl-dir, tls-crl-file,
     tls-rand-file as well as tls-verify.  Also see tls-features.  TLS is
     available if ‘+tls’ is included in features.

   Character sets
     [Option] Mail detects the character set of the terminal by using mechanisms
     that are controlled by the LC_CTYPE environment variable (in fact LC_ALL,
     LC_CTYPE, LANG, in that order, see there).  The internal variable
     ttycharset will be set to the detected terminal character set accordingly,
     and will thus show up in the output of commands like set and varshow.

     However, the user may give ttycharset a value during startup, making it
     possible to send mail in a completely “faked” locale environment, an option
     which can be used to generate and send for example 8-bit UTF-8 input data
     in a pure 7-bit US-ASCII ‘LC_ALL=C’ environment (an example of this can be
     found in the section On sending mail, and non-interactive mode).  Changing
     the value does not mean much beside that, because several aspects of the
     real character set are implied by the locale environment of the system,
     which stays unaffected by ttycharset.

     Messages and attachments which consist of 7-bit clean data will be
     classified as consisting of charset-7bit character data.  This is a problem
     if the ttycharset character set is a multibyte character set that is also
     7-bit clean.  For example, the Japanese character set ISO-2022-JP is 7-bit
     clean but capable to encode the rich set of Japanese Kanji, Hiragana and
     Katakana characters: in order to notify receivers of this character set the
     mail message must be MIME encoded so that the character set ISO-2022-JP can
     be advertised!  To achieve this, the variable charset-7bit must be set to
     ISO-2022-JP.  (Today a better approach regarding email is the usage of
     UTF-8, which uses 8-bit bytes for non-US-ASCII data.)

     If the [Option]al character set conversion capabilities are not available
     (features does not include the term ‘+iconv’), then ttycharset will be the
     only supported character set, it is simply assumed that it can be used to
     exchange 8-bit messages (over the wire an intermediate, configurable
     mime-encoding may be applied), and the rest of this section does not apply;
     it may however still be necessary to explicitly set it if automatic
     detection fails, since in that case it defaults to LATIN1 aka ISO-8859-1
     unless the operating system environment is known to always and exclusively
     support UTF-8 locales.

     [Option] When reading messages, their text is converted into ttycharset as
     necessary in order to display them on the user's terminal.  Unprintable
     characters and invalid byte sequences are detected and replaced by proper
     substitution characters.  Character set mappings for source character sets
     can be established with the command charsetalias, which may be handy to
     work around faulty character set catalogues (one could add a missing LATIN1
     to ISO-8859-1 mapping), or to enforce treatment of one character set as
     another one (maybe interpret LATIN1 as CP1252).  Also see
     charset-unknown-8bit to deal with another hairy aspect of message
     interpretation.

     When sending messages their parts and attachments are classified.  Whereas
     no character set conversion is performed on those parts which appear to be
     binary data, the character set being used must be declared within the MIME
     header of an outgoing text part if it contains characters that do not
     conform to the set of characters that are allowed by the email standards.
     Permissible values for character sets used in outgoing messages can be
     declared using the sendcharsets variable, and charset-8bit, which defines a
     catch-all last-resort fallback character set that is implicitly appended to
     the list of character sets in sendcharsets.

     When replying to a message and the variable reply-in-same-charset is set,
     then the character set of the message being replied to is tried first
     (still being a subject of charsetalias).  And it is also possible to make
     Mail work even more closely related to the current locale setting
     automatically by using the variable sendcharsets-else-ttycharset, please
     see there for more information.

     All the specified character sets are tried in order unless the conversion
     of the part or attachment succeeds.  If none of the tried (8-bit) character
     sets is capable to represent the content of the part or attachment, then
     the message will not be send and its text will optionally be saved in DEAD.
     If that is not acceptable, the variable mime-force-sendout can be set in
     order to force sending of non-convertible text as
     ‘application/octet-stream’ classified binary content instead; like this
     receivers still have the option to inspect message content (for example by
     setting mime-counter-evidence).

     In general, if a message saying “cannot convert from a to b” appears,
     either some characters are not appropriate for the currently selected
     (terminal) character set, or the needed conversion is not supported by the
     system.  In the first case, it is necessary to set an appropriate LC_CTYPE
     locale and/or the variable ttycharset.  The best results are usually
     achieved when Mail is run in a UTF-8 locale on an UTF-8 capable terminal,
     in which case the full Unicode spectrum of characters is available.  In
     this setup characters from various countries can be displayed, while it is
     still possible to use more simple character sets for sending to retain
     maximum compatibility with older mail clients.

     On the other hand the POSIX standard defines a locale-independent 7-bit
     “portable character set” that should be used when overall portability is an
     issue, the even more restricted subset named “portable filename character
     set” consists of A-Z, a-z, 0-9, period ‘.’, underscore ‘_’ and hyphen-minus
     ‘-’.

   Message states
     Mail differentiates in between several message states; the current state
     will be reflected in the summary of headers if the attrlist of the
     configured headline allows, and Specifying messages dependent on their
     state is possible.  When operating on the system inbox, or in any other
     primary system mailbox, special actions, like the automatic moving of
     messages to the secondary mailbox MBOX, may be applied when the mailbox is
     left (also implicitly by program termination, unless the command exit was
     used) – however, because this may be irritating to users which are used to
     “more modern” mail-user-agents, the provided global mail.rc template sets
     the internal hold and keepsave variables in order to suppress this
     behaviour.

     ‘new’     Message has neither been viewed nor moved to any other state.
               Such messages are retained even in the primary system mailbox.

     ‘unread’  Message has neither been viewed nor moved to any other state, but
               the message was present already when the mailbox has been opened
               last: Such messages are retained even in the primary system
               mailbox.

     ‘read’    The message has been processed by one of the following commands:
               ~f, ~m, ~F, ~M, copy, mbox, next, pipe, Print, print, top, Type,
               type, undelete.  The commands dp and dt will always try to
               automatically “step” and type the “next” logical message, and may
               thus mark multiple messages as read, the delete command will do
               so if the internal variable autoprint is set.

               Except when the exit command is used, messages that are in a
               primary system mailbox and are in ‘read’ state when the mailbox
               is left will be saved in the secondary mailbox MBOX unless the
               internal variable hold it set.

     ‘deleted’ The message has been processed by one of the following commands:
               delete, dp, dt.  Only undelete can be used to access such
               messages.

     ‘preserved’ The message has been processed by a preserve command and it
               will be retained in its current location.

     ‘saved’   The message has been processed by one of the following commands:
               save or write.  Unless when the exit command is used, messages
               that are in a primary system mailbox and are in ‘saved’ state
               when the mailbox is left will be deleted; they will be saved in
               the secondary mailbox MBOX when the internal variable keepsave is
               set.

     In addition to these message states, flags which otherwise have no
     technical meaning in the mail system except allowing special ways of
     addressing them when Specifying messages can be set on messages.  These
     flags are saved with messages and are thus persistent, and are portable
     between a set of widely used MUAs.

     answered  Mark messages as having been answered.

     draft     Mark messages as being a draft.

     flag      Mark messages which need special attention.

   Specifying messages
     [Only new quoting rules] COMMANDS which take Message list arguments, such
     as search, type, copy, and delete, can perform actions on a number of
     messages at once.  Specifying invalid messages, or using illegal syntax,
     will cause errors to be reported through the INTERNAL VARIABLES !, ^ERR and
     companions, as well as the command exit status ?.

     For example, ‘delete 1 2’ deletes the messages 1 and 2, whereas ‘delete
     1-5’ will delete the messages 1 through 5.  In sorted or threaded mode (see
     the sort command), ‘delete 1-5’ will delete the messages that are located
     between (and including) messages 1 through 5 in the sorted/threaded order,
     as shown in the headers summary.

     Errors can for example be ^ERR-BADMSG when requesting an invalid message,
     ^ERR-NOMSG if no applicable message can be found, ^ERR-CANCELED for missing
     informational data (mostly thread-related).  ^ERR-INVAL for invalid syntax
     as well as ^ERR-IO for input/output errors can happen.  The following
     special message names exist:

     .         The current message, the so-called “dot”.

     ;         The message that was previously the current message; needs to be
               quoted.

     ,         The parent message of the current message, that is the message
               with the Message-ID given in the ‘In-Reply-To:’ field or the last
               entry of the ‘References:’ field of the current message.

     -         The previous undeleted message, or the previous deleted message
               for the undelete command; In sorted or ‘thread’ed mode, the
               previous such message in the according order.

     +         The next undeleted message, or the next deleted message for the
               undelete command; In sorted or ‘thread’ed mode, the next such
               message in the according order.

     ^         The first undeleted message, or the first deleted message for the
               undelete command; In sorted or ‘thread’ed mode, the first such
               message in the according order.

     $         The last message; In sorted or ‘thread’ed mode, the last such
               message in the according order.  Needs to be quoted.

     &x        In ‘thread’ed sort mode, selects the message addressed with x,
               where x is any other message specification, and all messages from
               the thread that begins at it.  Otherwise it is identical to x.
               If x is omitted, the thread beginning with the current message is
               selected.

     *         All messages.

     `         All messages that were included in the Message list arguments of
               the previous command; needs to be quoted.  (A convenient way to
               read all new messages is to select them via ‘from :n’, as below,
               and then to read them in order with the default command — next —
               simply by successively typing ‘`’; for this to work showlast must
               be set.)

     x-y       An inclusive range of message numbers.  Selectors that may also
               be used as endpoints include any of .;-+^$.

     address   A case-insensitive “any substring matches” search against the
               ‘From:’ header, which will match addresses (too) even if showname
               is set (and POSIX says “any address as shown in a header summary
               shall be matchable in this form”); However, if the allnet
               variable is set, only the local part of the address is evaluated
               for the comparison, not ignoring case, and the setting of
               showname is completely ignored.  For finer control and match
               boundaries use the ‘@’ search expression.

     /string   All messages that contain string in the subject field (case
               ignored according to locale).  See also the searchheaders
               variable.  If string is empty, the string from the previous
               specification of that type is used again.

     [@name-list]@expr
               All messages that contain the given case-insensitive search
               expression;  If the [Option]al regular expression support is
               available expr will be interpreted as (an extended) one if any of
               the magic regular expression characters is seen.  If the optional
               @name-list part is missing the search is restricted to the
               subject field body, but otherwise name-list specifies a comma-
               separated list of header fields to search, for example

                     '@to,from,cc@Someone i ought to know'

               In order to search for a string that includes a ‘@’ (commercial
               at) character the name-list is effectively non-optional, but may
               be given as the empty string.  Also, specifying an empty search
               expression will effectively test for existence of the given
               header fields.  Some special header fields may be abbreviated:
               ‘f’, ‘t’, ‘c’, ‘b’ and ‘s’ will match ‘From’, ‘To’, ‘Cc’, ‘Bcc’
               and ‘Subject’, respectively and case-insensitively.
               [Option]ally, and just like expr, name-list will be interpreted
               as (an extended) regular expression if any of the magic regular
               expression characters is seen.

               The special names ‘header’ or ‘<’ can be used to search in (all
               of) the header(s) of the message, and the special names ‘body’ or
               ‘>’ and ‘text’ or ‘=’ will perform full text searches – whereas
               the former searches only the body, the latter also searches the
               message header ([v15 behaviour may differ] this mode yet brute
               force searches over the entire decoded content of messages,
               including administrativa strings).

               This specification performs full text comparison, but even with
               regular expression support it is almost impossible to write a
               search expression that safely matches only a specific address
               domain.  To request that the body content of the header is
               treated as a list of addresses, and to strip those down to the
               plain email address which the search expression is to be matched
               against, prefix the effective name-list with a tilde ‘~’:

                     '@~f,c@@a\.safe\.domain\.match$'

     :c        All messages of state or with matching condition ‘c’, where ‘c’
               is one or multiple of the following colon modifiers:

               a         answered messages (cf. the variable markanswered).
               d         ‘deleted’ messages (for the undelete and from commands
                         only).
               f         flagged messages.
               L         Messages with receivers that match mlsubscribed
                         addresses.
               l         Messages with receivers that match mlisted addresses.
               n         ‘new’ messages.
               o         Old messages (any not in state ‘read’ or ‘new’).
               r         ‘read’ messages.
               S         [Option] Messages with unsure spam classification (see
                         Handling spam).
               s         [Option] Messages classified as spam.
               t         Messages marked as draft.
               u         ‘unread’ messages.

     [Option] IMAP-style SEARCH expressions may also be used.  These consist of
     keywords and criterions, and because Message list arguments are split into
     tokens according to Shell-style argument quoting it is necessary to quote
     the entire IMAP search expression in order to ensure that it remains a
     single token.  This addressing mode is available with all types of mailbox
     folders; Mail will perform the search locally as necessary.  Strings must
     be enclosed by double quotation marks ‘"’ in their entirety if they contain
     whitespace or parentheses; within the quotes, only reverse solidus ‘\’ is
     recognized as an escape character.  All string searches are case-
     insensitive.  When the description indicates that the “envelope”
     representation of an address field is used, this means that the search
     string is checked against both a list constructed as

           '("name" "source" "local-part" "domain-part")'

     for each address, and the addresses without real names from the respective
     header field.  These search expressions can be nested using parentheses,
     see below for examples.

     (criterion)
               All messages that satisfy the given criterion.
     (criterion1 criterion2 ... criterionN)
               All messages that satisfy all of the given criteria.
     (or criterion1 criterion2)
               All messages that satisfy either criterion1 or criterion2, or
               both.  To connect more than two criteria using ‘or’
               specifications have to be nested using additional parentheses, as
               with ‘(or a (or b c))’, since ‘(or a b c)’ really means ‘((a or
               b) and c)’.  For a simple ‘or’ operation of independent criteria
               on the lowest nesting level, it is possible to achieve similar
               effects by using three separate criteria, as with ‘(a) (b) (c)’.
     (not criterion)
               All messages that do not satisfy criterion.
     (bcc "string")
               All messages that contain string in the envelope representation
               of the ‘Bcc:’ field.
     (cc "string")
               All messages that contain string in the envelope representation
               of the ‘Cc:’ field.
     (from "string")
               All messages that contain string in the envelope representation
               of the ‘From:’ field.
     (subject "string")
               All messages that contain string in the ‘Subject:’ field.
     (to "string")
               All messages that contain string in the envelope representation
               of the ‘To:’ field.
     (header name "string")
               All messages that contain string in the specified ‘Name:’ field.
     (body "string")
               All messages that contain string in their body.
     (text "string")
               All messages that contain string in their header or body.
     (larger size)
               All messages that are larger than size (in bytes).
     (smaller size)
               All messages that are smaller than size (in bytes).
     (before date)
               All messages that were received before date, which must be in the
               form ‘d[d]-mon-yyyy’, where ‘d’ denotes the day of the month as
               one or two digits, ‘mon’ is the name of the month – one of ‘Jan
               Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec’, and ‘yyyy’ is the
               year as four digits, for example ‘28-Dec-2012’.
     (on date)
               All messages that were received on the specified date.
     (since date)
               All messages that were received since the specified date.
     (sentbefore date)
               All messages that were sent on the specified date.
     (senton date)
               All messages that were sent on the specified date.
     (sentsince date)
               All messages that were sent since the specified date.
     ()        The same criterion as for the previous search.  This
               specification cannot be used as part of another criterion.  If
               the previous command line contained more than one independent
               criterion then the last of those criteria is used.

   On terminal control and line editor
     [Option] Terminal control through one of the standard UNIX libraries,
     Termcap Access Library (libtermcap, -ltermcap) or Terminal Information
     Library (libterminfo, -lterminfo), may be available.  For the TERMinal
     defined in the environment interactive usage aspects, for example Coloured
     display, and insight of cursor and function keys for the Mailx-Line-Editor
     (MLE), will be enhanced or enabled.  Library interaction can be disabled on
     a per-invocation basis via termcap-disable, whereas the internal variable
     termcap is always used as a preferred source of terminal capabilities.
     (For a usage example see the FAQ entry Not "defunctional", but the editor
     key does not work.)

     [Option] The built-in Mailx-Line-Editor (MLE) should work in all
     environments which comply to the ISO C standard ISO/IEC 9899/AMD1:1995
     (“ISO C90, Amendment 1”), and will support wide glyphs if possible (the
     necessary functionality had been removed from ISO C, but was included in
     X/Open Portability Guide Issue 4 (“XPG4”)).  Usage of a line editor in
     interactive mode can be prevented by setting line-editor-disable.
     Especially if the [Option]al terminal control support is missing setting
     entries in termcap will help shall the MLE misbehave, see there for more.
     The MLE can support a little bit of colour.

     [Option] If the history feature is available then input from line editor
     prompts will be saved in a history list that can be searched in and be
     expanded from.  Such saving can be prevented by prefixing input with any
     amount of whitespace.  Aspects of history, like allowed content and maximum
     size, as well as whether history shall be saved persistently, can be
     configured with the internal variables history-file, history-gabby,
     history-gabby-persist and history-size.  There also exists the macro hook
     on-history-addition which can be used to apply finer control on what enters
     history.

     The MLE supports a set of editing and control commands.  By default (as)
     many (as possible) of these will be assigned to a set of single-letter
     control codes, which should work on any terminal (and can be generated by
     holding the “control” key while pressing the key of desire, for example
     ‘control-D’).  If the [Option]al bind command is available then the MLE
     commands can also be accessed freely by assigning the command name, which
     is shown in parenthesis in the list below, to any desired key-sequence, and
     the MLE will instead and also use bind to establish its built-in key
     bindings (more of them if the [Option]al terminal control is available), an
     action which can then be suppressed completely by setting
     line-editor-no-defaults.  Shell-style argument quoting notation is used in
     the following:

     ‘\cA’     Go to the start of the line (mle-go-home).
     ‘\cB’     Move the cursor backward one character (mle-go-bwd).
     ‘\cC’     raise(3) ‘SIGINT’ (mle-raise-int).
     ‘\cD’     Forward delete the character under the cursor; quits Mail if used
               on the empty line unless the internal variable ignoreeof is set
               (mle-del-fwd).
     ‘\cE’     Go to the end of the line (mle-go-end).
     ‘\cF’     Move the cursor forward one character (mle-go-fwd).
     ‘\cG’     Cancel current operation, full reset.  If there is an active
               history search or tabulator expansion then this command will
               first reset that, reverting to the former line content; thus a
               second reset is needed for a full reset in this case (mle-reset).
     ‘\cH’     Backspace: backward delete one character (mle-del-bwd).
     ‘\cI’     [Only new quoting rules] Horizontal tabulator: try to expand the
               word before the cursor, supporting the usual Filename
               transformations (mle-complete; this is affected by
               mle-quote-rndtrip and line-editor-cpl-word-breaks).
     ‘\cJ’     Newline: commit the current line (mle-commit).
     ‘\cK’     Cut all characters from the cursor to the end of the line
               (mle-snarf-end).
     ‘\cL’     Repaint the line (mle-repaint).
     ‘\cN’     [Option] Go to the next history entry (mle-hist-fwd).
     ‘\cO’     ([Option]ally context-dependent) Invokes the command dt.
     ‘\cP’     [Option] Go to the previous history entry (mle-hist-bwd).
     ‘\cQ’     Toggle roundtrip mode shell quotes, where produced, on and off
               (mle-quote-rndtrip).  This setting is temporary, and will be
               forgotten once the command line is committed; also see shcodec.
     ‘\cR’     [Option] Complete the current line from (the remaining) older
               history entries (mle-hist-srch-bwd).
     ‘\cS’     [Option] Complete the current line from (the remaining) newer
               history entries (mle-hist-srch-fwd).
     ‘\cT’     Paste the snarf buffer (mle-paste).
     ‘\cU’     The same as ‘\cA’ followed by ‘\cK’ (mle-snarf-line).
     ‘\cV’     Prompts for a Unicode character (hexadecimal number without
               prefix, see vexpr) to be inserted (mle-prompt-char).  Note this
               command needs to be assigned to a single-letter control code in
               order to become recognized and executed during input of a key-
               sequence (only three single-letter control codes can be used for
               that shortcut purpose); this control code is then special-treated
               and thus cannot be part of any other sequence (because it will
               trigger the mle-prompt-char function immediately).
     ‘\cW’     Cut the characters from the one preceding the cursor to the
               preceding word boundary (mle-snarf-word-bwd).
     ‘\cX’     Move the cursor forward one word boundary (mle-go-word-fwd).
     ‘\cY’     Move the cursor backward one word boundary (mle-go-word-bwd).
     ‘\cZ’     raise(3) ‘SIGTSTP’ (mle-raise-tstp).
     ‘\c[’     Escape: reset a possibly used multibyte character input state
               machine and [Option]ally a lingering, incomplete key binding
               (mle-cancel).  This command needs to be assigned to a single-
               letter control code in order to become recognized and executed
               during input of a key-sequence (only three single-letter control
               codes can be used for that shortcut purpose).  This control code
               may also be part of a multi-byte sequence, but if a sequence is
               active and the very control code is currently also an expected
               input, then the active sequence takes precedence and will consume
               the control code.
     ‘\c\’     ([Option]ally context-dependent) Invokes the command ‘z+’.
     ‘\c]’     ([Option]ally context-dependent) Invokes the command ‘z$’.
     ‘\c^’     ([Option]ally context-dependent) Invokes the command ‘z0’.
     ‘\c_’     Cut the characters from the one after the cursor to the
               succeeding word boundary (mle-snarf-word-fwd).
     ‘\c?’     Backspace: mle-del-bwd.
     –         mle-bell: ring the audible bell.
     –         [Option] mle-clear-screen: move the cursor home and clear the
               screen.
     –         mle-fullreset: different to mle-reset this will immediately reset
               a possibly active search etc.
     –         mle-go-screen-bwd: move the cursor backward one screen width.
     –         mle-go-screen-fwd: move the cursor forward one screen width.
     –         mle-raise-quit: raise(3) ‘SIGQUIT’.

   Coloured display
     [Option] Colours and font attributes through ANSI a.k.a. ISO 6429 SGR
     (select graphic rendition) escape sequences are optionally supported.
     Usage of colours and font attributes solely depends upon the capability of
     the detected terminal type (TERM), and as fine-tuned through termcap.
     Colours and font attributes can be managed with the multiplexer command
     colour, and uncolour removes the given mappings.  Setting colour-disable
     suppresses usage of colour and font attribute sequences, while leaving
     established mappings unchanged.

     Whether actually applicable colour and font attribute sequences should also
     be generated when output is going to be paged through the external PAGER
     (also see crt) depends upon the setting of colour-pager, because pagers
     usually need to be configured in order to support ISO escape sequences.
     Knowledge of some widely used pagers is however built-in, and in a clean
     environment it is often enough to simply set colour-pager; please refer to
     that variable for more on this topic.

     It might make sense to conditionalize colour setup on interactive mode via
     if (‘terminal’ indeed means “interactive”):

           if terminal && "$features" =% +colour
             colour iso view-msginfo ft=bold,fg=green
             colour iso view-header ft=bold,fg=red (from|subject) # regex
             colour iso view-header fg=red

             uncolour iso view-header from,subject
             colour iso view-header ft=bold,fg=magenta,bg=cyan
             colour 256 view-header ft=bold,fg=208,bg=230 "subject,from"
             colour mono view-header ft=bold
             colour mono view-header ft=bold,ft=reverse subject,from
           endif

   Handling spam
     [Option] Mail can make use of several spam interfaces for the purpose of
     identification of, and, in general, dealing with spam messages.  A
     precondition of most commands in order to function is that the
     spam-interface variable is set to one of the supported interfaces.
     Specifying messages that have been identified as spam is possible via their
     (volatile) ‘is-spam’ state by using the ‘:s’ and ‘:S’ specifications, and
     their attrlist entries will be used when displaying the headline in the
     summary of headers.

     •   spamrate rates the given messages and sets their ‘is-spam’ flag
         accordingly.  If the spam interface offers spam scores these can be
         shown in headline by using the format ‘%$’.

     •   spamham, spamspam and spamforget will interact with the Bayesian filter
         of the chosen interface and learn the given messages as “ham” or
         “spam”, respectively; the last command can be used to cause
         “unlearning” of messages; it adheres to their current ‘is-spam’ state
         and thus reverts previous teachings.

     •   spamclear and spamset will simply set and clear, respectively, the
         mentioned volatile ‘is-spam’ message flag, without any interface
         interaction.

     The spamassassin(1) based spam-interface ‘spamc’ requires a running
     instance of the spamd(1) server in order to function, started with the
     option --allow-tell shall Bayesian filter learning be possible.

           $ spamd -i localhost:2142 -i /tmp/.spamsock -d [-L] [-l]
           $ spamd --listen=localhost:2142 --listen=/tmp/.spamsock \
               --daemonize [--local] [--allow-tell]

     Thereafter Mail can make use of these interfaces:

           $ mail -Sspam-interface=spamc -Sspam-maxsize=500000 \
               -Sspamc-command=/usr/local/bin/spamc \
               -Sspamc-arguments="-U /tmp/.spamsock" -Sspamc-user=
           or
           $ mail -Sspam-interface=spamc -Sspam-maxsize=500000 \
               -Sspamc-command=/usr/local/bin/spamc \
               -Sspamc-arguments="-d localhost -p 2142" -Sspamc-user=

     Using the generic filter approach allows usage of programs like
     bogofilter(1).  Here is an example, requiring it to be accessible via PATH:

           $ mail -Sspam-interface=filter -Sspam-maxsize=500000 \
               -Sspamfilter-ham="bogofilter -n" \
               -Sspamfilter-noham="bogofilter -N" \
               -Sspamfilter-nospam="bogofilter -S" \
               -Sspamfilter-rate="bogofilter -TTu 2>/dev/null" \
               -Sspamfilter-spam="bogofilter -s" \
               -Sspamfilter-rate-scanscore="1;^(.+)$"

     Because messages must exist on local storage in order to be scored (or used
     for Bayesian filter training), it is possibly a good idea to perform the
     local spam check last.  Spam can be checked automatically when opening
     specific folders by setting a specialized form of the internal variable
     folder-hook.

           define spamdelhook {
             # Server side DCC
             spamset (header x-dcc-brand-metrics "bulk")
             # Server-side spamassassin(1)
             spamset (header x-spam-flag "YES")
             del :s # TODO we HAVE to be able to do `spamrate :u ! :sS'
             move :S +maybe-spam
             spamrate :u
             del :s
             move :S +maybe-spam
           }
           set folder-hook-SOMEFOLDER=spamdelhook

     See also the documentation for the variables spam-interface, spam-maxsize,
     spamc-command, spamc-arguments, spamc-user, spamfilter-ham,
     spamfilter-noham, spamfilter-nospam, spamfilter-rate and
     spamfilter-rate-scanscore.

COMMANDS
     Mail reads input in lines.  An unquoted reverse solidus ‘\’ at the end of a
     command line “escapes” the newline character: it is discarded and the next
     line of input is used as a follow-up line, with all leading whitespace
     removed; once an entire line is completed, the whitespace characters space,
     tabulator, newline as well as those defined by the variable ifs are removed
     from the beginning and end.  Placing any whitespace characters at the
     beginning of a line will prevent a possible addition of the command line to
     the [Option]al history.

     The beginning of such input lines is then scanned for the name of a known
     command: command names may be abbreviated, in which case the first command
     that matches the given prefix will be used.  Command modifiers may prefix a
     command in order to modify its behaviour.  A name may also be a
     commandalias, which will become expanded until no more expansion is
     possible.  Once the command that shall be executed is known, the remains of
     the input line will be interpreted according to command-specific rules,
     documented in the following.

     This behaviour is different to the sh(1)ell, which is a programming
     language with syntactic elements of clearly defined semantics, and
     therefore capable to sequentially expand and evaluate individual elements
     of a line.  Mail will never be able to handle ‘? set one=value two=$one’ in
     a single statement, because the variable assignment is performed by the
     command (set), not the language.

     A list of all commands in lookup order is dumped by the command list.
     [Option]ally the command help (or ?), when given an argument, will show a
     documentation string for the command matching the expanded argument, as in
     ‘?t’, which should be a shorthand of ‘?type’; with these documentation
     strings both commands support a more verbose listing mode which includes
     the argument type of the command and other information which applies; a
     handy suggestion might thus be:

           ? define __xv {
             # Before v15: need to enable sh(1)ell-style on _entire_ line!
             localopts yes;wysh set verbose;ignerr eval "${@}";return ${?}
           }
           ? commandalias xv '\call __xv'
           ? xv help set

   Command modifiers
     Commands may be prefixed by none to multiple command modifiers.  Some
     command modifiers can be used with a restricted set of commands only, the
     verbose version of list will ([Option]ally) show which modifiers apply.

     The modifier reverse solidus \, to be placed first, prevents
         commandalias expansions on the remains of the line, for example ‘\echo’
         will always evaluate the command echo, even if an (command)alias of the
         same name exists.  commandalias content may itself contain further
         command modifiers, including an initial reverse solidus to prevent
         further expansions.

     The modifier ignerr indicates that any error generated by the following
         command should be ignored by the state machine and not cause a program
         exit with enabled errexit or for the standardized exit cases in posix
         mode.  ?, one of the INTERNAL VARIABLES, will be set to the real exit
         status of the command regardless.

     •   local will alter the called command to apply changes only temporarily,
         local to block-scope, and can thus only be used inside of a defined
         macro or an account definition.  Specifying it implies the modifier
         wysh.  Block-scope settings will not be inherited by macros deeper in
         the call chain, and will be garbage collected once the current block is
         left.  To record and unroll changes in the global scope use the command
         localopts.

     •   scope does yet not implement any functionality.

     •   u does yet not implement any functionality.

     Some commands support the vput modifier: if used, they expect the name
         of a variable, which can itself be a variable, i.e., shell expansion is
         applied, as their first argument, and will place their computation
         result in it instead of the default location (it is usually written to
         standard output).

         The given name will be tested for being a valid sh(1) variable name,
         and may therefore only consist of upper- and lowercase characters,
         digits, and the underscore; the hyphen-minus may be used as a non-
         portable extension; digits may not be used as first, hyphen-minus may
         not be used as last characters.  In addition the name may either not be
         one of the known INTERNAL VARIABLES, or must otherwise refer to a
         writable (non-boolean) value variable.  The actual put operation may
         fail nonetheless, for example if the variable expects a number argument
         only a number will be accepted.  Any error during these operations
         causes the command as such to fail, and the error number ! will be set
         to ^ERR-NOTSUP, the exit status ? should be set to ‘-1’, but some
         commands deviate from the latter, which is documented.

     Last, but not least, the modifier wysh can be used for some old and
         established commands to choose the new Shell-style argument quoting
         rules over the traditional Old-style argument quoting.  This modifier
         is implied if v15-compat is set to a non-empty value.

   Old-style argument quoting
     [v15 behaviour may differ] This section documents the traditional and POSIX
     standardized style of quoting non-message list arguments to commands which
     expect this type of arguments: whereas still used by the majority of such
     commands, the new Shell-style argument quoting may be available even for
     those via wysh, one of the Command modifiers.  Nonetheless care must be
     taken, because only new commands have been designed with all the
     capabilities of the new quoting rules in mind, which can, for example
     generate control characters.

           An argument can be enclosed between paired double-quotes
               ‘"argument"’ or single-quotes ‘'argument'’; any whitespace, shell
               word expansion, or reverse solidus characters (except as
               described next) within the quotes are treated literally as part
               of the argument.  A double-quote will be treated literally within
               single-quotes and vice versa.  Inside such a quoted string the
               actually used quote character can be used nonetheless by escaping
               it with a reverse solidus ‘\’, as in ‘"y\"ou"’.

           An argument that is not enclosed in quotes, as above, can usually
               still contain space characters if those spaces are reverse
               solidus escaped, as in ‘you\ are’.

           A reverse solidus outside of the enclosing quotes is discarded
               and the following character is treated literally as part of the
               argument.

   Shell-style argument quoting
     sh(1)ell-style, and therefore POSIX standardized, argument parsing and
     quoting rules are used by most commands.  [v15 behaviour may differ] Most
     new commands only support these new rules and are flagged [Only new quoting
     rules], some elder ones can use them with the command modifier wysh; in the
     future only this type of argument quoting will remain.

     A command line is parsed from left to right and an input token is completed
     whenever an unquoted, otherwise ignored, metacharacter is seen.
     Metacharacters are vertical bar |, ampersand &, semicolon ;, as well as all
     characters from the variable ifs, and / or space, tabulator, newline.  The
     additional metacharacters left and right parenthesis (, ) and less-than and
     greater-than signs <, > that the sh(1) supports are not used, and are
     treated as ordinary characters: for one these characters are a vivid part
     of email addresses, and it seems highly unlikely that their function will
     become meaningful to Mail.

           Compatibility note: [v15 behaviour may differ] Please note that even
           many new-style commands do not yet honour ifs to parse their
           arguments: whereas the sh(1)ell is a language with syntactic elements
           of clearly defined semantics, Mail parses entire input lines and
           decides on a per-command base what to do with the rest of the line.
           This also means that whenever an unknown command is seen all that
           Mail can do is cancellation of the processing of the remains of the
           line.

           It also often depends on an actual subcommand of a multiplexer
           command how the rest of the line should be treated, and until v15 we
           are not capable to perform this deep inspection of arguments.
           Nonetheless, at least the following commands which work with
           positional parameters fully support ifs for an almost shell-
           compatible field splitting: call, call_if, read, vpospar, xcall.

     Any unquoted number sign ‘#’ at the beginning of a new token starts a
     comment that extends to the end of the line, and therefore ends argument
     processing.  An unquoted dollar sign ‘$’ will cause variable expansion of
     the given name, which must be a valid sh(1)ell-style variable name (see
     vput): INTERNAL VARIABLES as well as ENVIRONMENT (shell) variables can be
     accessed through this mechanism, brace enclosing the name is supported
     (i.e., to subdivide a token).

     Whereas the metacharacters space, tabulator, newline only complete an input
     token, vertical bar |, ampersand & and semicolon ; also act as control
     operators and perform control functions.  For now supported is semicolon ;,
     which terminates a single command, therefore sequencing the command line
     and making the remainder of the line a subject to reevaluation.  With
     sequencing, multiple command argument types and quoting rules may therefore
     apply to a single line, which can become problematic before v15: e.g., the
     first of the following will cause surprising results.

           ? echo one; set verbose; echo verbose=$verbose.
           ? echo one; wysh set verbose; echo verbose=$verbose.

     Quoting is a mechanism that will remove the special meaning of
     metacharacters and reserved words, and will prevent expansion.  There are
     four quoting mechanisms: the escape character, single-quotes, double-quotes
     and dollar-single-quotes:

           The literal value of any character can be preserved by preceding
               it with the escape character reverse solidus ‘\’.

           Arguments which are enclosed in ‘'single-quotes'’ retain their
               literal value.  A single-quote cannot occur within single-quotes.

           The literal value of all characters enclosed in ‘"double-quotes"’
               is retained, with the exception of dollar sign ‘$’, which will
               cause variable expansion, as above, backquote (grave accent) ‘`’,
               (which not yet means anything special), reverse solidus ‘\’,
               which will escape any of the characters dollar sign ‘$’ (to
               prevent variable expansion), backquote (grave accent) ‘`’,
               double-quote ‘"’ (to prevent ending the quote) and reverse
               solidus ‘\’ (to prevent escaping, i.e., to embed a reverse
               solidus character as-is), but has no special meaning otherwise.

           Arguments enclosed in ‘$'dollar-single-quotes'’ extend normal
               single quotes in that reverse solidus escape sequences are
               expanded as follows:

               ‘\a’    bell control character (ASCII and ISO-10646 BEL).
               ‘\b’    backspace control character (ASCII and ISO-10646 BS).
               ‘\E’    escape control character (ASCII and ISO-10646 ESC).
               ‘\e’    the same.
               ‘\f’    form feed control character (ASCII and ISO-10646 FF).
               ‘\n’    line feed control character (ASCII and ISO-10646 LF).
               ‘\r’    carriage return control character (ASCII and ISO-10646
                       CR).
               ‘\t’    horizontal tabulator control character (ASCII and
                       ISO-10646 HT).
               ‘\v’    vertical tabulator control character (ASCII and ISO-10646
                       VT).
               ‘\\’    emits a reverse solidus character.
               ‘\'’    single quote.
               ‘\"’    double quote (escaping is optional).
               ‘\NNN’  eight-bit byte with the octal value ‘NNN’ (one to three
                       octal digits), optionally prefixed by an additional ‘0’.
                       A 0 byte will suppress further output for the quoted
                       argument.
               ‘\xHH’  eight-bit byte with the hexadecimal value ‘HH’ (one or
                       two hexadecimal characters, no prefix, see vexpr).  A 0
                       byte will suppress further output for the quoted
                       argument.
               ‘\UHHHHHHHH’
                       the Unicode / ISO-10646 character with the hexadecimal
                       codepoint value ‘HHHHHHHH’ (one to eight hexadecimal
                       characters) — note that Unicode defines the maximum
                       codepoint ever to be supported as ‘0x10FFFF’ (in planes
                       of ‘0xFFFF’ characters each).  This escape is only
                       supported in locales that support Unicode (see Character
                       sets), in other cases the sequence will remain unexpanded
                       unless the given code point is ASCII compatible or (if
                       the [Option]al character set conversion is available) can
                       be represented in the current locale.  The character NUL
                       will suppress further output for the quoted argument.
               ‘\uHHHH’
                       Identical to ‘\UHHHHHHHH’ except it takes only one to
                       four hexadecimal characters.
               ‘\cX’   Emits the non-printable (ASCII and compatible) C0 control
                       codes 0 (NUL) to 31 (US), and 127 (DEL).  Printable
                       representations of ASCII control codes can be created by
                       mapping them to a different, visible part of the ASCII
                       character set.  Adding the number 64 achieves this for
                       the codes 0 to 31, here 7 (BEL): ‘7 + 64 = 71 = G’.  The
                       real operation is a bitwise logical XOR with 64 (bit 7
                       set, see vexpr), thus also covering code 127 (DEL), which
                       is mapped to 63 (question mark): ‘? vexpr ^ 127 64’.

                       Whereas historically circumflex notation has often been
                       used for visualization purposes of control codes, as in
                       ‘^G’, the reverse solidus notation has been standardized:
                       ‘\cG’.  Some control codes also have standardized
                       (ISO-10646, ISO C) aliases, as shown above (‘\a’, ‘\n’,
                       ‘\t’ etc) : whenever such an alias exists it will be used
                       for display purposes.  The control code NUL (‘\c@’, a
                       non-standard extension) will suppress further output for
                       the remains of the token (which may extend beyond the
                       current quote), or, depending on the context, the remains
                       of all arguments for the current command.
               ‘\$NAME’
                       Non-standard extension: expand the given variable name,
                       as above.  Brace enclosing the name is supported.
               ‘\`{command}’
                       Not yet supported, just to raise awareness: Non-standard
                       extension.

     Caveats:

           ? echo 'Quotes '${HOME}' and 'tokens" differ!"# no comment
           ? echo Quotes ${HOME} and tokens differ! # comment
           ? echo Don"'"t you worry$'\x21' The sun shines on us. $'\u263A'

   Message list arguments
     Many commands operate on message list specifications, as documented in
     Specifying messages.  The argument input is first split into individual
     tokens via Shell-style argument quoting, which are then interpreted as the
     mentioned specifications.  If no explicit message list has been specified,
     many commands will search for and use the next message forward that
     satisfies the commands' requirements, and if there are no messages forward
     of the current message, the search proceeds backwards; if there are no good
     messages at all to be found, an error message is shown and the command is
     aborted.  The verbose output of the command list will indicate whether a
     command searches for a default message, or not.

   Raw data arguments for codec commands
     A special set of commands, which all have the string “codec” in their name,
     like addrcodec, shcodec, urlcodec, take raw string data as input, which
     means that the content of the command input line is passed completely
     unexpanded and otherwise unchanged: like this the effect of the actual
     codec is visible without any noise of possible shell quoting rules etc.,
     i.e., the user can input one-to-one the desired or questionable data.  To
     gain a level of expansion, the entire command line can be evaluated first,
     for example

           ? vput shcodec res encode /usr/Schönes Wetter/heute.txt
           ? echo $res
           $'/usr/Sch\u00F6nes Wetter/heute.txt'
           ? shcodec d $res
           $'/usr/Sch\u00F6nes Wetter/heute.txt'
           ? eval shcodec d $res
           /usr/Schönes Wetter/heute.txt

   Filename transformations
     Filenames, where expected, and unless documented otherwise, are
     subsequently subject to the following filename transformations, in
     sequence:

           If the given name is a registered shortcut, it will be replaced
               with the expanded shortcut.  This step is mostly taken for
               folders only.

           The filename is matched against the following patterns or
               strings.  But for plus +file folder expansion this step is mostly
               taken for folders only.

               #      (Number sign) is expanded to the previous file.
               %      (Percent sign) is replaced by the invoking user's primary
                      system mailbox, which either is the (itself expandable)
                      inbox if that is set, the standardized absolute pathname
                      indicated by MAIL if that is set, or a built-in compile-
                      time default otherwise.  When opening a folder the used
                      name is actively checked for being a primary mailbox,
                      first against inbox, then against MAIL.
               %user  Expands to the primary system mailbox of user (and never
                      the value of inbox, regardless of its actual setting).
               &      (Ampersand) is replaced with the invoking user's secondary
                      mailbox, the MBOX.
               +file  Refers to a file in the folder directory (if that variable
                      is set).
               %:filespec Expands to the same value as filespec, but has special
                      meaning when used with, for example, the command folder:
                      the file will be treated as a primary system mailbox by,
                      among others, the mbox and save commands, meaning that
                      messages that have been read in the current session will
                      be moved to the MBOX mailbox instead of simply being
                      flagged as read.

           Meta expansions may be applied to the resulting filename, as
               allowed by the operation and applicable to the resulting access
               protocol (also see On URL syntax and credential lookup).  For the
               file-protocol, a leading tilde ‘~’ character will be replaced by
               the expansion of HOME, except when followed by a valid user name,
               in which case the home directory of the given user is used
               instead.

               A shell expansion as if specified in double-quotes (see
               Shell-style argument quoting) may be applied, so that any
               occurrence of ‘$VARIABLE’ (or ‘${VARIABLE}’) will be replaced by
               the expansion of the variable, if possible; INTERNAL VARIABLES as
               well as ENVIRONMENT (shell) variables can be accessed through
               this mechanism.

               Shell pathname wildcard pattern expansions (glob(7)) may be
               applied as documented.  If the fully expanded filename results in
               multiple pathnames and the command is expecting only one file, an
               error results.

               In interactive context, in order to allow simple value acceptance
               (via “ENTER”), arguments will usually be displayed in a properly
               quoted form, so a file ‘diet\ is \curd.txt’ may be displayed as
               ‘'diet\ is \curd.txt'’.

   Commands
     The following commands are available:

     !         Executes the SHELL command which follows, replacing unescaped
               exclamation marks with the previously executed command if the
               internal variable bang is set.  This command supports vput as
               documented in Command modifiers, and manages the error number !.
               A 0 or positive exit status ? reflects the exit status of the
               command, negative ones that an error happened before the command
               was executed, or that the program did not exit cleanly, but maybe
               due to a signal: the error number is ^ERR-CHILD, then.

               In conjunction with the vput modifier the following special cases
               exist: a negative exit status occurs if the collected data could
               not be stored in the given variable, which is a ^ERR-NOTSUP error
               that should otherwise not occur.  ^ERR-CANCELED indicates that no
               temporary file could be created to collect the command output at
               first glance.  In case of catchable out-of-memory situations
               ^ERR-NOMEM will occur and Mail will try to store the empty
               string, just like with all other detected error conditions.

     #         The comment-command causes the entire line to be ignored.  Note:
               this really is a normal command which' purpose is to discard its
               arguments, not a “comment-start” indicating special character,
               which means that for example trailing comments on a line are not
               possible (except for commands which use Shell-style argument
               quoting).

     +         Goes to the next message in sequence and types it (like “ENTER”).

     -         Display the preceding message, or the n'th previous message if
               given a numeric argument n.

     =         Shows the message number of the current message (the “dot”) when
               used without arguments, that of the given list otherwise.  Output
               numbers will be separated from each other with the first
               character of ifs, and followed by the first character of if-ws,
               if that is not empty and not identical to the first.  If that
               results in no separation at all a space character is used.  This
               command supports vput (see Command modifiers), and manages the
               error number !.

     ?         [Option] Show a brief summary of commands.  [Option] Given an
               argument a synopsis for the command in question is shown instead;
               commands can be abbreviated in general and this command can be
               used to see the full expansion of an abbreviation including the
               synopsis, try, for example ‘?h’, ‘?hel’ and ‘?help’ and see how
               the output changes.  To avoid that aliases are resolved the
               modifier \ can be prepended to the argument, but note it must be
               quoted.  This mode also supports a more verbose output, which
               will provide the information documented for list.

     |         A synonym for the pipe command.

     account, unaccount
               (ac, una) Creates, selects or lists (an) account(s).  Accounts
               are special incarnations of defined macros and group commands and
               variable settings which together usually arrange the environment
               for the purpose of creating an email account.  Different to
               normal macros settings which are covered by localopts – here by
               default enabled! – will not be reverted before the account is
               changed again.  The special account ‘null’ (case-insensitive)
               always exists, and all but it can be deleted by the latter
               command, and in one operation with the special name ‘*’.  Also
               for all but it a possibly set on-account-cleanup hook is called
               once they are left, including program exit.

               Without arguments a listing of all defined accounts is shown.
               With one argument the given account is activated: the system
               inbox of that account will be activated (as via folder), a
               possibly installed folder-hook will be run, and the internal
               variable account will be updated.  The two argument form is
               identical to defining a macro as via define:

                     account myisp {
                       set folder=~/mail inbox=+syste.mbox record=+sent.mbox
                       set from='(My Name) myname@myisp.example'
                       set mta=smtp://mylogin@smtp.myisp.example
                     }

     addrcodec
               Perform email address codec transformations on raw-data argument,
               rather according to email standards (RFC 5322; [v15 behaviour may
               differ] will furtherly improve).  Supports vput (see Command
               modifiers), and manages the error number !.  The first argument
               must be either [+[+[+]]]e[ncode], d[ecode], s[kin] or skinl[ist]
               and specifies the operation to perform on the rest of the line.

               Decoding will show how a standard-compliant MUA will display the
               given argument, which should be an email address.  Please be
               aware that most MUAs have difficulties with the address
               standards, and vary wildly when (comments) in parenthesis,
               “double-quoted” strings, or quoted-pairs, as below, become
               involved.  [v15 behaviour may differ] Mail currently does not
               perform decoding when displaying addresses.

               Skinning is identical to decoding but only outputs the plain
               address, without any string, comment etc. components.  Another
               difference is that it may fail with the error number ! set to
               ^ERR-INVAL if decoding fails to find a(n) (valid) email address,
               in which case the unmodified input will be output again.

               skinlist first performs a skin operation, and thereafter checks a
               valid address for whether it is a registered mailing list (see
               mlist and mlsubscribe), eventually reporting that state in the
               error number ! as ^ERR-EXIST.  (This state could later become
               overwritten by an I/O error, though.)

               Encoding supports four different modes, lesser automated versions
               can be chosen by prefixing one, two or three plus signs: the
               standard imposes a special meaning on some characters, which thus
               have to be transformed to so-called quoted-pairs by pairing them
               with a reverse solidus ‘\’ in order to remove the special
               meaning; this might change interpretation of the entire argument
               from what has been desired, however!  Specify one plus sign to
               remark that parenthesis shall be left alone, two for not turning
               double quotation marks into quoted-pairs, and three for also
               leaving any user-specified reverse solidus alone.  The result
               will always be valid, if a successful exit status is reported
               ([v15 behaviour may differ] the current parser fails this
               assertion for some constructs).  [v15 behaviour may differ]
               Addresses need to be specified in between angle brackets ‘<’, ‘>’
               if the construct becomes more difficult, otherwise the current
               parser will fail; it is not smart enough to guess right.

                     ? addrc enc "Hey, you",<diet@exam.ple>\ out\ there
                     "\"Hey, you\", \\ out\\ there" <diet@exam.ple>
                     ? addrc d "\"Hey, you\", \\ out\\ there" <diet@exam.ple>
                     "Hey, you", \ out\ there <diet@exam.ple>
                     ? addrc s "\"Hey, you\", \\ out\\ there" <diet@exam.ple>
                     diet@exam.ple

     alias, unalias
               [Only new quoting rules](a, una) Define or list, and remove,
               respectively, address aliases.  Address aliases are a method of
               creating personal distribution lists that map a single alias name
               to none to multiple receivers; aliases are expanded after message
               composing is completed.  The latter command removes all given
               aliases, the special name asterisk ‘*’ will remove all existing
               aliases.  When used without arguments the former shows a list of
               all currently known aliases, with one argument only the target(s)
               of the given one.  When given two arguments, hyphen-minus ‘-’
               being the first, the target(s) of the second is/are expanded
               recursively.

               In all other cases the given address alias is newly defined or
               will be appended to: target arguments must either be valid alias
               names, or any other address type.  Recursive expansion of (what
               looks like) alias name(s) targets can be prevented by prefixing
               the target with the modifier reverse solidus \.  A valid alias
               name conforms to mta-aliases syntax, but follow-up characters can
               also be the number sign ‘#’, colon ‘’:, commercial at ‘@,’
               exclamation mark ‘!’, period ‘.’ as well as “any character that
               has the high bit set”.  The dollar sign ‘$’ may be the last
               character.  The number sign may need be quoted to avoid
               misinterpretation as the shell comment character.

               [v15 behaviour may differ] Unfortunately the colon is currently
               not supported, as it interferes with normal address parsing
               rules.  [v15 behaviour may differ] Such high bit characters will
               likely cause warnings at the moment for the same reasons why
               colon is unsupported; also, in the future locale dependent
               character set validity checks will be performed.

     alternates, unalternates
               [Only new quoting rules] (alt) Manage a list of alternate
               addresses or names of the active user, members of which will be
               removed from recipient lists (except one).  There is a set of
               implicit alternates which is formed of the values of LOGNAME,
               from, sender and reply-to.  from will not be used if sender is
               set.  The latter command removes the given list of alternates,
               the special name ‘*’ will discard all existing alternate names.

               The former command manages the error number !.  It shows the
               current set of alternates when used without arguments; in this
               mode only it also supports vput (see Command modifiers).
               Otherwise the given arguments (after being checked for validity)
               are appended to the list of alternate names; in posix mode they
               replace that list instead.

     answered, unanswered
               Take a message lists and mark each message as (not) having been
               answered.  Messages will be marked answered when being replyd to
               automatically if the markanswered variable is set.  See the
               section Message states.

     bind, unbind
               [Option][Only new quoting rules] The bind command extends the MLE
               (see On terminal control and line editor) with freely
               configurable key bindings.  The latter command removes from the
               given context the given key binding, both of which may be
               specified as a wildcard ‘*’, so that ‘unbind * *’ will remove all
               bindings of all contexts.  Due to initialization order unbinding
               will not work for built-in key bindings upon program startup,
               however: please use line-editor-no-defaults for this purpose
               instead.

               With zero arguments, or with a context name the former command
               shows all key bindings (of the given context; an asterisk ‘*’
               will iterate over all contexts); a more verbose listing will be
               produced if either of debug or verbose are set.  With two or more
               arguments a specific binding is shown, or (re)established: the
               first argument is the context to which the binding shall apply,
               the second argument is a comma-separated list of the “keys” which
               form the binding.  Further arguments will be joined to form the
               expansion, and cause the binding to be created or updated.  To
               indicate that a binding shall not be auto-committed, but that the
               expansion shall instead be furtherly editable by the user, a
               commercial at ‘@’ (that will be removed) can be placed last in
               the expansion, from which leading and trailing whitespace will
               finally be removed.  Reverse solidus cannot be used as the last
               character of expansion.  An empty expansion will be rejected.

               Contexts define when a binding applies, i.e., a binding will not
               be seen unless the context for which it is defined for is
               currently active.  This is not true for the shared binding
               ‘base’, which is the foundation for all other bindings and as
               such always applies, its bindings, however, only apply
               secondarily.  The available contexts are the shared ‘base’, the
               ‘default’ context which is used in all not otherwise documented
               situations, and ‘compose’, which applies to compose mode only.

               Bindings are specified as a comma-separated list of byte-
               sequences, where each list entry corresponds to one “key”
               (press).  Byte sequence boundaries will be forcefully terminated
               after bind-inter-byte-timeout milliseconds, whereas key sequences
               can be timed out via bind-inter-key-timeout.  A list entry may,
               indicated by a leading colon character ‘:’, also refer to the
               name of a terminal capability; several dozen names are compiled
               in and may be specified either by their terminfo(5), or, if
               existing, by their termcap(5) name, regardless of the actually
               used [Option]al terminal control library.  But any capability may
               be used, as long as the name is resolvable by the [Option]al
               control library, or was defined via the internal variable
               termcap.  Input sequences are not case-normalized, an exact match
               is required to update or remove a binding.  It is advisable to
               use an initial escape or other control character (like ‘\cA’) for
               user (as opposed to purely terminal capability based) bindings in
               order to avoid ambiguities; it also reduces search time.
               Examples:

                     ? bind base a,b echo one
                     ? bind base $'\E',d mle-snarf-word-fwd # Esc(ape)
                     ? bind base $'\E',$'\c?' mle-snarf-word-bwd # Esc,Delete
                     ? bind default $'\cA',:khome,w 'echo Editable binding@'
                     ? bind default a,b,c rm -irf / @  # Also editable
                     ? bind default :kf1 File %
                     ? bind compose :kf1 ~v

               Note that the entire comma-separated list is first parsed (over)
               as a shell-token with whitespace as the field separator, then
               parsed and expanded for real with comma as the field separator,
               therefore whitespace needs to be properly quoted, see Shell-style
               argument quoting.  Using Unicode reverse solidus escape sequences
               renders a binding defunctional if the locale does not support
               Unicode (see Character sets), and using terminal capabilities
               does so if no (corresponding) terminal control support is
               (currently) available.  Adding, deleting or modifying a key
               binding invalidates the internal prebuilt lookup tree, it will be
               recreated as necessary: this process will be visualized in most
               verbose as well as in debug mode.

               The following terminal capability names are built-in and can be
               used in terminfo(5) or (if available) the two-letter termcap(5)
               notation.  See the respective manual for a list of capabilities.
               The program infocmp(1) can be used to show all the capabilities
               of TERM or the given terminal type; using the -x flag will also
               show supported (non-standard) extensions.

               kbs or kb       Backspace.
               kdch1 or kD     Delete character.
               kDC or *4       — shifted variant.
               kel or kE       Clear to end of line.
               kext or @9      Exit.
               kich1 or kI     Insert character.
               kIC or #3       — shifted variant.
               khome or kh     Home.
               kHOM or #2      — shifted variant.
               kend or @7      End.
               knp or kN       Next page.
               kpp or kP       Previous page.
               kcub1 or kl     Left cursor (with more modifiers: see below).
               kLFT or #4      — shifted variant.
               kcuf1 or kr     Right cursor (ditto).
               kRIT or %i      — shifted variant.
               kcud1 or kd     Down cursor (ditto).
               kDN             — shifted variant (only terminfo).
               kcuu1 or ku     Up cursor (ditto).
               kUP             — shifted variant (only terminfo).
               kf0 or k0       Function key 0.  Add one for each function key up
                               to kf9 and k9, respectively.
               kf10 or k;      Function key 10.
               kf11 or F1      Function key 11.  Add one for each function key
                               up to kf19 and F9, respectively.

               Some terminals support key-modifier combination extensions, e.g.,
               ‘Alt+Shift+xy’.  For example, the delete key, kdch1: in its
               shifted variant, the name is mutated to kDC, then a number is
               appended for the states ‘Alt’ (kDC3), ‘Shift+Alt’ (kDC4),
               ‘Control’ (kDC5), ‘Shift+Control’ (kDC6), ‘Alt+Control’ (kDC7),
               finally ‘Shift+Alt+Control’ (kDC8).  The same for the left cursor
               key, kcub1: KLFT, KLFT3, KLFT4, KLFT5, KLFT6, KLFT7, KLFT8.

     call      [Only new quoting rules] Calls the given macro, which must have
               been created via define (see there for more), otherwise an
               ^ERR-NOENT error occurs.  Calling macros recursively will at some
               time excess the stack size limit, causing a hard program
               abortion; if recursively calling a macro is the last command of
               the current macro, consider to use the command xcall, which will
               first release all resources of the current macro before replacing
               the current macro with the called one.

     call_if   Identical to call if the given macro has been created via define,
               but does not fail nor warn if the macro does not exist.

     cd        Synonym for chdir.

     certsave  [Option] Only applicable to S/MIME signed messages.  Takes an
               optional message list and a filename and saves the certificates
               contained within the message signatures to the named file in both
               human-readable and PEM format.  The certificates can later be
               used to send encrypted messages to the respective message senders
               by setting smime-encrypt-USER@HOST variables.

     charsetalias, uncharsetalias
               [Only new quoting rules] Manage alias mappings for (conversion
               of) Character sets.  Alias processing is not performed for
               INTERNAL VARIABLES, for example charset-8bit, and mappings are
               ineffective if character set conversion is not available
               (features does not announce ‘+iconv’).  Expansion happens
               recursively for cases where aliases point to other aliases
               (built-in loop limit: 8).

               The latter command deletes all aliases given as arguments, or all
               at once when given the asterisk ‘*’.  The former shows the list
               of all currently defined aliases if used without arguments, or
               the target of the given single argument; when given two
               arguments, hyphen-minus ‘-’ being the first, the second is
               instead expanded recursively.  In all other cases the given
               arguments are treated as pairs of character sets and their
               desired target alias name, creating new or updating already
               existing aliases.

     chdir     [Only new quoting rules](ch) Change the working directory to HOME
               or the given argument.  Synonym for cd.

     collapse, uncollapse
               Only applicable to ‘thread’ed sort mode.  Takes a message list
               and makes all replies to these messages invisible in header
               summaries, except for ‘new’ messages and the “dot”.  Also when a
               message with collapsed replies is displayed, all of these are
               automatically uncollapsed.  The latter command undoes collapsing.

     colour, uncolour
               [Option][Only new quoting rules] Manage colour mappings of and
               for a Coloured display.  Without arguments the former shows all
               currently defined mappings.  Otherwise a colour type is expected
               (case-insensitively), it must be one of ‘256’ for 256-colour
               terminals, ‘8’, ‘ansi’ or ‘iso’ for the standard 8-colour ANSI /
               ISO 6429 colour palette, and ‘1’ or ‘mono’ for monochrome
               terminals, which only support (some) font attributes.  Without
               further arguments the list of all currently defined mappings of
               the given type is shown (here the special ‘all’ or ‘*’ also show
               all currently defined mappings).

               Otherwise the second argument defines the mappable slot, the
               third argument a (comma-separated list of) colour and font
               attribute specification(s), and the optionally supported fourth
               argument can be used to specify a precondition: if conditioned
               mappings exist they are tested in (creation) order unless a
               (case-insensitive) match has been found, and the default mapping
               (if any has been established) will only be chosen as a last
               resort.  The types of available preconditions depend on the
               mappable slot, the following of which exist:

               Mappings prefixed with ‘mle-’ are used for the [Option]al built-
               in Mailx-Line-Editor (MLE, see On terminal control and line
               editor) and do not support preconditions.

               mle-position   This mapping is used for the position indicator
                              that is visible when a line cannot be fully
                              displayed on the screen.
               mle-prompt     Used for the prompt.
               mle-error      Used for the occasionally appearing error
                              indicator that is joined onto prompt.  [v15
                              behaviour may differ] Also used for error messages
                              written on standard error .

               Mappings prefixed with ‘sum-’ are used in header summaries, and
               they all understand the preconditions ‘dot’ (the current message)
               and ‘older’ for elder messages (only honoured in conjunction with
               datefield-markout-older).

               sum-dotmark    This mapping is used for the “dotmark” that can be
                              created with the ‘%>’ or ‘%<’ formats of the
                              variable headline.
               sum-header     For the complete header summary line except the
                              “dotmark” and the thread structure.
               sum-thread     For the thread structure which can be created with
                              the ‘%i’ format of the variable headline.

               Mappings prefixed with ‘view-’ are used when displaying messages.

               view-from_     This mapping is used for so-called ‘From_’ lines,
                              which are MBOX file format specific header lines
                              (also see mbox-rfc4155).
               view-header    For header lines.  A comma-separated list of
                              headers to which the mapping applies may be given
                              as a precondition; if the [Option]al regular
                              expression support is available then if any of the
                              magic regular expression characters is seen the
                              precondition will be evaluated as (an extended)
                              one.
               view-msginfo   For the introductional message info line.
               view-partinfo  For MIME part info lines.

               The following (case-insensitive) colour definitions and font
               attributes are understood, multiple of which can be specified in
               a comma-separated list:

               ft=  a font attribute: ‘bold’, ‘reverse’ or ‘underline’.  It is
                    possible (and often applicable) to specify multiple font
                    attributes for a single mapping.

               fg=  foreground colour attribute: ‘black’, ‘blue’, ‘green’,
                    ‘red’, ‘brown’, ‘magenta’, ‘cyan’ or ‘white’.  To specify a
                    256-colour mode a decimal number colour specification in the
                    range 0 to 255, inclusive, is supported, and interpreted as
                    follows:

                    0 - 7      the standard ISO 6429 colours, as above.
                    8 - 15     high intensity variants of the standard colours.
                    16 - 231   216 colours in tuples of 6.
                    232 - 255  grayscale from black to white in 24 steps.

                          #!/bin/sh -
                          fg() { printf "\033[38;5;${1}m($1)"; }
                          bg() { printf "\033[48;5;${1}m($1)"; }
                          i=0
                          while [ $i -lt 256 ]; do fg $i; i=$(($i + 1)); done
                          printf "\033[0m\n"
                          i=0
                          while [ $i -lt 256 ]; do bg $i; i=$(($i + 1)); done
                          printf "\033[0m\n"

               bg=  background colour attribute (see fg= for possible values).

               The command uncolour will remove for the given colour type (the
               special type ‘*’ selects all) the given mapping; if the optional
               precondition argument is given only the exact tuple of mapping
               and precondition is removed.  The special name ‘*’ will remove
               all mappings (no precondition allowed), thus ‘uncolour * *’ will
               remove all established mappings.

     commandalias, uncommandalias
               [Only new quoting rules] Define or list, and remove,
               respectively, command aliases.  An (command)alias can be used
               everywhere a normal command can be used, but always takes
               precedence: any arguments that are given to the command alias are
               joined onto the alias expansion, and the resulting string forms
               the command line that is, in effect, executed.  The latter
               command removes all given aliases, the special name asterisk ‘*’
               will remove all existing aliases.  When used without arguments
               the former shows a list of all currently known aliases, with one
               argument only the expansion of the given one.

               With two or more arguments a command alias is defined or updated:
               the first argument is the name under which the remaining command
               line should be accessible, the content of which can be just about
               anything.  An alias may itself expand to another alias, but to
               avoid expansion loops further expansion will be prevented if an
               alias refers to itself or if an expansion depth limit is reached.
               Explicit expansion prevention is available via reverse solidus \,
               one of the Command modifiers.

                     ? commandalias xx
                     mail: `commandalias': no such alias: xx
                     ? commandalias xx echo hello,
                     ? commandalias xx
                     commandalias xx 'echo hello,'
                     ? xx
                     hello,
                     ? xx world
                     hello, world

     Copy      (C) Similar to copy, but copy the messages to a file named after
               the local part of the sender of the first message instead of
               taking a filename argument; outfolder is inspected to decide on
               the actual storage location.

     copy      (c) Copy messages to the named file and do not mark them as being
               saved; otherwise identical to save.

     csop      [Only new quoting rules] A multiplexer command which provides C-
               style string operations on 8-bit bytes without a notion of locale
               settings and character sets, effectively assuming ASCII data.
               For numeric and other operations refer to vexpr.  vput, one of
               the Command modifiers, is supported.  The error result is ‘-1’
               for usage errors and numeric results, the empty string otherwise;
               missing data errors, as for unsuccessful searches, result in the
               ! error number being set to ^ERR-NODATA.  Where the question mark
               ‘?’ modifier suffix is supported, a case-insensitive (ASCII
               mapping) operation mode is supported; the keyword ‘case’ is
               optional so that ‘find?’ and ‘find?case’ are identical.

               length    Queries the length of the given argument.

               hash, hash32 Calculates a hash value of the given argument.  The
                         latter will return a 32-bit result regardless of host
                         environment.  ‘?’ modifier suffix is supported.  These
                         use Chris Torek's hash algorithm, the resulting hash
                         value is bit mixed as shown by Bret Mulvey.

               find      Search for the second in the first argument.  Shows the
                         resulting 0-based offset shall it have been found.  ‘?’
                         modifier suffix is supported.

               substring Creates a substring of its first argument.  The
                         optional second argument is the 0-based starting
                         offset, a negative one counts from the end; the
                         optional third argument specifies the length of the
                         desired result, a negative length leaves off the given
                         number of bytes at the end of the original string; by
                         default the entire string is used.  This operation
                         tries to work around faulty arguments (set verbose for
                         error logs), but reports them via the error number ! as
                         ^ERR-OVERFLOW.

               trim      Trim away whitespace characters from both ends of the
                         argument.

               trim-front Trim away whitespace characters from the begin of the
                         argument.

               trim-end  Trim away whitespace characters from the end of the
                         argument.

     cwd       Show the name of the current working directory, as reported by
               getcwd(3).  Supports vput (see Command modifiers).  The return
               status is tracked via ?.

     Decrypt   [Option] For unencrypted messages this command is identical to
               Copy; Encrypted messages are first decrypted, if possible, and
               then copied.

     decrypt   [Option] For unencrypted messages this command is identical to
               copy; Encrypted messages are first decrypted, if possible, and
               then copied.

     define, undefine
               The latter command deletes the given macro, the special name ‘*’
               will discard all existing macros.  Deletion of (a) macro(s) can
               be performed from within running (a) macro(s), including self-
               deletion.  Without arguments the former command prints the
               current list of macros, including their content, otherwise it
               defines a macro, replacing an existing one of the same name as
               applicable.

               A defined macro can be invoked explicitly by using the call,
               call_if and xcall commands, or implicitly if a macro hook is
               triggered, for example a folder-hook.  Execution of a macro body
               can be stopped from within by calling return.

               Temporary macro block-scope variables can be created or deleted
               with the local command modifier in conjunction with the commands
               set and unset, respectively.  To enforce unrolling of changes
               made to (global) INTERNAL VARIABLES the command localopts can be
               used instead; its covered scope depends on how (i.e., “as what”:
               normal macro, folder hook, hook, account switch) the macro is
               invoked.

               Inside a called macro, the given positional parameters are
               implicitly local to the macro's scope, and may be accessed via
               the variables *, @, # and 1 and any other positive unsigned
               decimal number less than or equal to #.  Positional parameters
               can be shifted, or become completely replaced, removed etc. via
               vpospar.  A helpful command for numeric computation and string
               evaluations is vexpr, csop offers C-style byte string operations.

                     define name {
                       command1
                       command2
                       ...
                       commandN
                     }

                     define exmac {
                       echo Parameter 1 of ${#} is ${1}, all: ${*} / ${@}
                       return 1000 0
                     }
                     call exmac Hello macro exmac!
                     echo ${?}/${!}/${^ERRNAME}

     delete, undelete
               (d, u) Marks the given message list as being or not being
               ‘deleted’, respectively; if no argument has been specified then
               the usual search for a visible message is performed, as
               documented for Message list arguments, showing only the next
               input prompt if the search fails.  Deleted messages will neither
               be saved in the secondary mailbox MBOX nor will they be available
               for most other commands.  If the autoprint variable is set, the
               new “dot” or the last message restored, respectively, is
               automatically typed; also see dp, dt.

     digmsg    [Only new quoting rules] Digging (information out of) messages is
               possible through digmsg objects, which can be created for the
               given message number; in compose mode the hyphen-minus ‘-’ will
               instead open the message that is being composed.  If a hyphen-
               minus is given as the optional third argument then output will be
               generated on the standard output channel instead of being subject
               to consumation by the readsh (here better than read or readall)
               command.

               The objects may be removed again by giving the same identifier
               used for creation; this step could be omitted: objects will be
               automatically closed when the active mailbox or the compose mode
               is left, respectively.  In all other use cases the second
               argument is an object identifier, and the third and all following
               arguments are interpreted as via ~^ (see COMMAND ESCAPES):

                     ? vput = msgno; digmsg create $msgno
                     ? digmsg $msgno header list;   readall x;   echon $x
                     210 Subject From To Message-ID References In-Reply-To
                     ? digmsg $msgno header show Subject;readall x;echon $x
                     212 Subject

                     ? digmsg remove $msgno

     discard   (di) Identical to ignore.  Superseded by the multiplexer
               headerpick.

     dp, dt    Delete the given messages and automatically type the new “dot” if
               one exists, regardless of the setting of autoprint.

     dotmove   Move the “dot” up or down by one message when given ‘+’ or ‘-’
               argument, respectively.

     draft, undraft
               Take message lists and mark each given message as being draft, or
               not being draft, respectively, as documented in the section
               Message states.

     echo      [Only new quoting rules](ec) Echoes arguments to standard output
               and writes a trailing newline, whereas the otherwise identical
               echon does not.  Shell-style argument quoting is used, Filename
               transformations are applied to the expanded arguments.  This
               command also supports vput as documented in Command modifiers,
               and manages the error number !: if data is stored in a variable
               then the return value reflects the length of the result string in
               case of success and is ‘-1’ on error.

     echoerr   [Only new quoting rules] Identical to echo, but the message is
               written to standard error, and prefixed by log-prefix.  Also see
               echoerrn.  In interactive sessions the [Option]al message ring
               queue for errors will be used instead, if available and vput was
               not used.

     echon     [Only new quoting rules] Identical to echo, but does not write or
               store a trailing newline.

     echoerrn  [Only new quoting rules] Identical to echoerr, but does not write
               or store a trailing newline.

     edit      (e) Point the text EDITOR at each message from the given list in
               turn.  Modified contents are discarded unless the writebackedited
               variable is set, and are not used unless the mailbox can be
               written to and the editor returns a successful exit status.
               visual can be used instead for a more display oriented editor.

     elif      Part of the if (see there for more), elif, else, endif
               conditional — if the condition of a preceding if was false, check
               the following condition and execute the following block if it
               evaluates true.

     else      (el) Part of the if (see there for more), elif, else, endif
               conditional — if none of the conditions of the preceding if and
               elif commands was true, the else block is executed.

     endif     (en) Marks the end of an if (see there for more), elif, else,
               endif conditional execution block.

     environ   [Only new quoting rules] There is a strict separation in between
               INTERNAL VARIABLES and the program ENVIRONMENT, which is
               inherited by child processes.  Some variables of the latter are
               however vivid for program operation, their purpose is known,
               therefore they have been integrated transparently into handling
               of the former, as accessible via set and unset.  To integrate any
               other environment variable, and/or to export internal variables
               into the process environment where they normally are not, a link
               needs to become established with this command, for example

                     environ link PERL5LIB TZ

               Afterwards changing such variables with set will cause automatic
               updates of the environment, too.  Sufficient system support
               provided (it was in BSD as early as 1987, and is standardized
               since Y2K) removing such variables with unset will remove them
               also from the environment, but in any way the knowledge they ever
               have been linked will be lost.  This implies that localopts may
               cause loss of such links.

               The subcommand unlink removes an existing link without otherwise
               touching variables, the set and unset subcommands are identical
               to set and unset, but additionally update the program environment
               accordingly; removing a variable breaks any freely established
               link.

     errors    [Option] Since Mail uses the console as a user interface it can
               happen that messages scroll by too fast to become recognized.
               Therefore an error log queue is available which can be managed by
               errors: show or no argument will display and clear the queue,
               clear will only clear the queue.  The queue is finite: if its
               maximum size is reached any new message replaces the eldest.
               There are also the variables ^ERRQUEUE-COUNT and
               ^ERRQUEUE-EXISTS.

     eval      [Only new quoting rules] Construct a command by concatenating the
               arguments, separated with a single space character, and then
               evaluate the result.  This command passes through the exit status
               ? and error number ! of the evaluated command; also see call.

                     define xxx {
                       echo "xxx arg <$1>"
                       shift
                       if $# -gt 0
                         \xcall xxx "$@"
                       endif
                     }
                     define yyy {
                       eval "$@ ' ball"
                     }
                     call yyy '\call xxx' "b\$'\t'u ' "
                     call xxx arg <b      u>
                     call xxx arg <  >
                     call xxx arg <ball>

     exit      (ex or x) Exit from Mail without changing the active mailbox and
               skip any saving of messages in the secondary mailbox MBOX, as
               well as a possibly tracked line editor history-file.  A possibly
               set on-account-cleanup will be invoked, however.  The optional
               status number argument will be passed through to exit(3).  [v15
               behaviour may differ] For now it can happen that the given status
               will be overwritten, later this will only occur if a later error
               needs to be reported onto an otherwise success indicating status.

     File      (Fi) Like folder, but open the mailbox read-only.

     file      (fi) See folder.

     filetype, unfiletype
               [Only new quoting rules] Define, list, and remove, respectively,
               file handler hooks, which provide (shell) commands that enable
               Mail to load and save MBOX files from and to files with the
               registered file extensions, as shown and described for folder.
               The extensions are used case-insensitively, yet the auto-
               completion feature of for example folder will only work case-
               sensitively.  An intermediate temporary file will be used to
               store the expanded data.  The latter command will remove hooks
               for all given extensions, asterisk ‘*’ will remove all existing
               handlers.

               When used without arguments the former shows a list of all
               currently defined file hooks, with one argument the expansion of
               the given alias.  Otherwise three arguments are expected, the
               first specifying the file extension for which the hook is meant,
               and the second and third defining the load- and save commands to
               deal with the file type, respectively, both of which must read
               from standard input and write to standard output.  Changing hooks
               will not affect already opened mailboxes ([v15 behaviour may
               differ] except below).  [v15 behaviour may differ] For now too
               much work is done, and files are oftened read in twice where once
               would be sufficient: this can cause problems if a filetype is
               changed while such a file is opened; this was already so with the
               built-in support of .gz etc. in Heirloom, and will vanish in v15.
               [v15 behaviour may differ] For now all handler strings are passed
               to the SHELL for evaluation purposes; in the future a ‘!’ prefix
               to load and save commands may mean to bypass this shell instance:
               placing a leading space will avoid any possible
               misinterpretations.

                     ? filetype bz2 'bzip2 -dc' 'bzip2 -zc' \
                         gz 'gzip -dc' 'gzip -c'  xz 'xz -dc' 'xz -zc' \
                         zst 'zstd -dc' 'zstd -19 -zc' \
                         zst.pgp 'gpg -d | zstd -dc' 'zstd -19 -zc | gpg -e'
                     ? set record=+sent.zst.pgp

     flag, unflag
               Take message lists and mark the messages as being flagged, or not
               being flagged, respectively, for urgent/special attention.  See
               the section Message states.

     Folder    (Fold) Like folder, but open the mailbox read-only.

     folder    (fold) Open a new, or show status information of the current
               mailbox.  If an argument is given, changes (such as deletions)
               will be written out, a new mailbox will be opened, the internal
               variables mailbox-resolved and mailbox-display will be updated, a
               set according folder-hook is executed, and optionally a summary
               of headers is displayed if the variable header is set.

               Filename transformations will be applied to the name argument,
               and ‘protocol://’ prefixes are, i.e., URL (see On URL syntax and
               credential lookup) syntax is understood, as in
               ‘mbox:///tmp/somefolder’.  If a protocol prefix is used the
               mailbox type is fixated, otherwise opening none-existing folders
               uses the protocol defined in newfolders.

               For the protocols mbox and file (MBOX database), as well as eml
               (electronic mail message [v15 behaviour may differ] read-only)
               the list of all registered filetypes is traversed to check
               whether hooks shall be used to load (and save) data from (and to)
               the given name.  Changing hooks will not affect already opened
               mailboxes.  For example, the following creates hooks for the
               gzip(1) compression tool and a combined compressed and encrypted
               format:

                     ? filetype \
                         gzip 'gzip -dc' 'gzip -c' \
                         zst.pgp 'gpg -d | zstd -dc' 'zstd -19 -zc | gpg -e'

               For historic reasons filetypes provide limited (case-sensitive)
               auto-completion capabilities.  For example ‘mbox.gz’ will be
               found for ‘? file mbox’, provided that corresponding handlers are
               installed.  It will neither find ‘mbox.GZ’ nor ‘mbox.Gz’ however,
               but an explicit ‘? file mbox.GZ’ will find and use the handler
               for ‘gz’.  [v15 behaviour may differ] The latter mode can only be
               used for MBOX files.

               EML files consist of only one mail message, [v15 behaviour may
               differ] and can only be opened read-only.  When reading MBOX
               files tolerant POSIX rules are used by default.  Invalid message
               boundaries that can be found quite often in historic MBOX files
               will be complained about (even more with debug ): in this case
               the method described for mbox-rfc4155 can be used to create a
               valid MBOX database from the invalid input.

               MBOX databases and EML files will always be protected via file-
               region locks (fcntl(2)) during file operations to protect against
               concurrent modifications.  [Option] An MBOX inbox (MAIL) or
               primary system mailbox will also be protected by so-called
               dotlock files, the traditional way of mail spool file locking:
               for any file ‘x’ a lock file ‘x.lock’ will be created during the
               synchronization, in the same directory and with the same user and
               group identities as the file of interest — as necessary created
               by an external privileged dotlock helper.  dotlock-disable
               disables dotlock files.  Also see FAQ: Howto handle stale dotlock
               files.

               [Option] If no protocol has been fixated, and name refers to a
               directory with the subdirectories ‘tmp’, ‘new’ and ‘cur’, then it
               is treated as a folder in “Maildir” format.  The maildir format
               stores each message in its own file, and has been designed so
               that file locking is not necessary when reading or writing files.

               [Option]ally URLs can be used to access network resources,
               securely via Encrypted network communication, if so supported.
               Network communication socket timeouts are configurable via
               socket-connect-timeout.  All network traffic may be proxied over
               a SOCKS server via socks-proxy.

                     [v15-compat]
                     protocol://[user[:password]@]host[:port][/path]
                     [no v15-compat] protocol://[user@]host[:port][/path]

               [Option]ally supported network protocols are pop3 (POP3) and
               pop3s (POP3 with TLS encrypted transport), imap and imaps.  The
               [/path] part is valid only for IMAP; there it defaults to INBOX.
               Network URLs require a special encoding as documented in the
               section On URL syntax and credential lookup.

     folders   Lists the names of all folders below the given argument or
               folder.  For file-based protocols LISTER will be used for display
               purposes.

     Followup, followup
               (Compose mode)(F,fo) Similar to Reply, and reply, respectively,
               but save the message in a file named after the local part of the
               (first) recipient's address, possibly overwriting record, and
               honouring outfolder.  Also see Copy and Save.

     Forward   (Compose mode) Similar to forward, but saves the message in a
               file named after the local part of the recipient's address
               (instead of in record).

     forward   (Compose mode) Take a message list and the address of a
               recipient, subject to fullnames, to whom the messages are sent.
               The text of the original message is included in the new one,
               enclosed by the values of forward-inject-head and
               forward-inject-tail.  content-description-forwarded-message is
               inspected.  The list of included headers can be filtered with the
               ‘forward’ slot of the white- and blacklisting command headerpick.
               Only the first part of a multipart message is included but for
               forward-as-attachment.

               This may generate the errors ^ERR-DESTADDRREQ if no receiver has
               been specified, or was rejected by expandaddr policy, ^ERR-IO if
               an I/O error occurs, ^ERR-NOTSUP if a necessary character set
               conversion fails, and ^ERR-INVAL for other errors.  It can also
               fail with errors of Specifying messages.  Any error stops
               processing of further messages.

     from      (f) Takes a list of message specifications and displays a summary
               of their message headers, exactly as via headers, making the
               first message of the result the new “dot” (the last message if
               showlast is set).  An alias of this command is search.  Also see
               Specifying messages.

     Fwd       [Obsolete] Alias for Forward.

     fwd       [Obsolete] Alias for forward.

     fwdignore
               [Obsolete] Superseded by the multiplexer headerpick.

     fwdretain
               [Obsolete] Superseded by the multiplexer headerpick.

     ghost, unghost
               [Obsolete] Replaced by commandalias, uncommandalias.

     headerpick, unheaderpick
               [Only new quoting rules] Multiplexer command to manage white- and
               blacklisting selections of header fields for a variety of
               applications.  Without arguments the set of contexts that have
               settings is displayed.  When given arguments, the first argument
               is the context to which the command applies, one of (case-
               insensitive) ‘type’ for display purposes (for example type),
               ‘save’ for selecting which headers shall be stored persistently
               when save, copy, move or even decrypting messages (note that MIME
               related etc. header fields should not be ignored in order to not
               destroy usability of the message in this case), ‘forward’ for
               stripping down messages when forwarding message (has no effect if
               forward-as-attachment is set), and ‘top’ for defining user-
               defined set of fields for the command top.

               The current settings of the given context are displayed if it is
               the only argument.  A second argument denotes the type of
               restriction that is to be chosen, it may be (a case-insensitive
               prefix of) ‘retain’ or ‘ignore’ for white- and blacklisting
               purposes, respectively.  Establishing a whitelist suppresses
               inspection of the corresponding blacklist.

               If no further argument is given the current settings of the given
               type will be displayed, otherwise the remaining arguments specify
               header fields, which [Option]ally may be given as regular
               expressions, to be added to the given type.  The special wildcard
               field (asterisk, ‘*’) will establish a (fast) shorthand setting
               which covers all fields.

               The latter command always takes three or more arguments and can
               be used to remove selections, i.e., from the given context, the
               given type of list, all the given headers will be removed, the
               special argument ‘*’ will remove all headers.

     headers   (h) Show the current group of headers, the size of which depends
               on the variable screen in interactive mode, and the format of
               which can be defined with headline.  If a message-specification
               is given the group of headers containing the first message
               therein is shown and the message at the top of the screen becomes
               the new “dot”; the last message is targeted if showlast is set.

     help      (hel) A synonym for ?.

     history   [Option] Without arguments or when given show all history entries
               are shown (this mode also supports a more verbose output).  load
               will replace the list of entries with the content of
               history-file, and save will dump the current list to said file,
               replacing former content.  clear will delete all history entries.
               The argument can also be a signed decimal NUMBER, which will
               select and evaluate the respective history entry, and move it to
               the top of the history; a negative number is used as an offset to
               the current command so that ‘-1’ will select the last command,
               the history top.  An entry may be deleted by giving delete
               followed by a NUMBER.  Also see On terminal control and line
               editor.

     hold      (ho, also preserve) Takes a message list and marks each message
               therein to be saved in the user's system inbox instead of in the
               secondary mailbox MBOX.  Does not override the delete command.
               Mail deviates from the POSIX standard with this command, because
               a next command issued after hold will display the following
               message, not the current one.

     if        (i) Part of the if, elif, else, endif conditional execution
               construct — if the given condition is true then the encapsulated
               block is executed.  The POSIX standard only supports the (case-
               insensitive) conditions ‘r’eceive and ‘s’end, the remaining are
               non-portable extensions.  [v15 behaviour may differ] In
               conjunction with the wysh command prefix(es) Shell-style argument
               quoting and more test operators are available.

                     if receive
                       commands ...
                     else
                       commands ...
                     endif

               Further (case-insensitive) one-argument conditions are ‘t’erminal
               which evaluates to true in interactive terminal sessions (running
               with standard input or standard output attached to a terminal,
               and none of the “quickrun” command line options -e, -H and -L
               have been used), as well as any boolean value (see INTERNAL
               VARIABLES for textual boolean representations) to mark an
               enwrapped block as “never execute” or “always execute”.
               (Remarks: condition syntax errors skip all branches until endif.)

               [no v15-compat] and without wysh: It is possible to check
               INTERNAL VARIABLES as well as ENVIRONMENT variables for existence
               or compare their expansion against a user given value or another
               variable by using the ‘$’ (“variable next”) conditional trigger
               character; a variable on the right hand side may be signalled
               using the same mechanism.  Variable names may be enclosed in a
               pair of matching braces.  When this mode has been triggered,
               several operators are available ([v15-compat] and wysh: they are
               always available, and there is no trigger: variables will have
               been expanded by the shell-compatible parser before the if etc.
               command sees them).

               [v15-compat] Two argument conditions.  Variables can be tested
               for existence and expansion: ‘-N’ will test whether the given
               variable exists, so that ‘-N editalong’ will evaluate to true
               when editalong is set, whereas ‘-Z editalong’ will if it is not.
               ‘-n "$editalong"’ will be true if the variable is set and expands
               to a non-empty string, ‘-z $'\$editalong'’ only if the expansion
               is empty, whether the variable exists or not.  The remaining
               conditions take three arguments.

               Integer operators treat the arguments on the left and right hand
               side of the operator as integral numbers and compare them
               arithmetically.  It is an error if any of the operands is not a
               valid integer, an empty argument (which implies it had been
               quoted) is treated as if it were 0.  Via the question mark ‘?’
               modifier suffix a saturated operation mode is available where
               numbers will linger at the minimum or maximum possible value,
               instead of overflowing (or trapping), the keyword ‘saturated’ is
               optional, ‘==?’, ‘==?satu’ and ‘==?saturated’ are therefore
               identical.  Available operators are ‘-lt’ (less than), ‘-le’
               (less than or equal to), ‘-eq’ (equal), ‘-ne’ (not equal), ‘-ge’
               (greater than or equal to), and ‘-gt’ (greater than).

               String and regular expression data operators compare the left and
               right hand side according to their textual content.  Unset
               variables are treated as the empty string.  Via the question mark
               ‘?’ modifier suffix a case-insensitive operation mode is
               available, the keyword ‘case’ is optional, ‘==?’ and ‘==?case’
               are identical.

               Available string operators are ‘<’ (less than), ‘<=’ (less than
               or equal to), ‘==’ (equal), ‘!=’ (not equal), ‘>=’ (greater than
               or equal to), ‘>’ (greater than), ‘=%’ (is substring of) and ‘!%’
               (is not substring of).  By default these operators work on bytes
               and (therefore) do not take into account character set specifics.
               If the case-insensitivity modifier has been used, case is ignored
               according to the rules of the US-ASCII encoding, i.e., bytes are
               still compared.

               When the [Option]al regular expression support is available, the
               additional string operators ‘=~’ and ‘!~’ can be used.  They
               treat the right hand side as an extended regular expression that
               is matched according to the active locale (see Character sets),
               i.e., character sets should be honoured correctly.

               Conditions can be joined via AND-OR lists (where the AND operator
               is ‘&&’ and the OR operator is ‘||’), which have equal precedence
               and will be evaluated with left associativity, thus using the
               same syntax that is known for the sh(1).  It is also possible to
               form groups of conditions and lists by enclosing them in pairs of
               brackets ‘[ ... ]’, which may be interlocked within each other,
               and also be joined via AND-OR lists.

               The results of individual conditions and entire groups may be
               modified via unary operators: the unary operator ‘!’ will reverse
               the result.

                     wysh set v15-compat=yes # with value: automatic "wysh"!
                     if -N debug;echo *debug* set;else;echo not;endif
                     if [ "$ttycharset" == UTF-8 ] || \
                         [ "$ttycharset" ==?case UTF8 ]
                       echo *ttycharset* is UTF-8, the former case-sensitive!
                     endif
                     set t1=one t2=one
                     if [ "${t1}" == "${t2}" ]
                       echo These two variables are equal
                     endif
                     if "$features" =% +regex && "$TERM" =~?case "^xterm.*"
                       echo ..in an X terminal
                     endif
                     if [ [ true ] && [ [ "${debug}" != '' ] || \
                         [ "$verbose" != '' ] ] ]
                       echo Noisy, noisy
                     endif
                     if true && [ -n "$debug" || -n "${verbose}" ]
                       echo Left associativity, as is known from the shell
                     endif

     ignore    (ig) Identical to discard.  Superseded by the multiplexer
               headerpick.

     list      Shows the names of all available commands, in command lookup
               order.  [Option] In conjunction with a set variable verbose
               additional information will be provided for each command: the
               argument type will be indicated, the documentation string will be
               shown, and the set of command flags will show up:

               ‘`local'’    command supports the command modifier local.
               ‘`vput'’     command supports the command modifier vput.
               ‘*!*’        the error number is tracked in !.
               ‘needs-box’  whether the command needs an active mailbox, a
                            folder.
               ‘ok:’        indicators whether command is ...
                            ‘batch/interactive’
                                          usable in interactive or batch mode
                                          (-#).
                            ‘send-mode’   usable in send mode.
                            ‘subprocess’  allowed to be used when running in a
                                          subprocess instance, for example from
                                          within a macro that is called via
                                          on-compose-splice.
               ‘not ok:’    indicators whether command is not ...
                            ‘compose-mode’  available in compose mode.
                            ‘startup’       available during program startup,
                                            like in Resource files.
               ‘gabby’      The command produces history-gabby history entries.

     localopts
               Enforce change localization of environ (linked) ENVIRONMENT as
               well as (global) INTERNAL VARIABLES, meaning that their state
               will be reverted to the former one once the “covered scope” is
               left.  Just like the command modifier local, which provides
               block-scope localization for some commands (instead), it can only
               be used inside of macro definition blocks introduced by account
               or define.  The covered scope of an account is left once a
               different account is activated, and some macros, notably
               folder-hooks, use their own specific notion of covered scope,
               here it will be extended until the folder is left again.

               This setting stacks up: i.e., if ‘macro1’ enables change
               localization and calls ‘macro2’, which explicitly resets
               localization, then any value changes within ‘macro2’ will still
               be reverted when the scope of ‘macro1’ is left.  (Caveats: if in
               this example ‘macro2’ changes to a different account which sets
               some variables that are already covered by localizations, their
               scope will be extended, and in fact leaving the account will
               (thus) restore settings in (likely) global scope which actually
               were defined in a local, macro private context!)

               This command takes one or two arguments, the optional first one
               specifies an attribute that may be one of scope, which refers to
               the current scope and is thus the default, call, which causes any
               macro that is being called to be started with localization
               enabled by default, as well as call-fixate, which (if enabled)
               disallows any called macro to turn off localization: like this it
               can be ensured that once the current scope regains control, any
               changes made in deeper levels have been reverted.  The latter two
               are mutually exclusive, and neither affects xcall.  The (second)
               argument is interpreted as a boolean (string, see INTERNAL
               VARIABLES) and states whether the given attribute shall be turned
               on or off.

                     define temporary_settings {
                       set possibly_global_option1
                       localopts on
                       set localized_option1
                       set localized_option2
                       localopts scope off
                       set possibly_global_option2
                     }

     Lfollowup, Lreply
               (Compose mode) Reply to messages that come in via known (mlist)
               or subscribed (mlsubscribe) mailing lists, or pretend to do so
               (see Mailing lists): on top of the usual followup and reply,
               respectively, functionality this will actively resort and even
               remove message recipients in order to generate a message that is
               supposed to be sent to a mailing list.  For example it will also
               implicitly generate a ‘Mail-Followup-To:’ header if that seems
               useful, regardless of the setting of the variable followup-to.
               For more documentation please refer to On sending mail, and non-
               interactive mode.

               This may generate the errors ^ERR-DESTADDRREQ if no receiver has
               been specified, ^ERR-PERM if some addressees where rejected by
               expandaddr, ^ERR-IO if an I/O error occurs, ^ERR-NOTSUP if a
               necessary character set conversion fails, and ^ERR-INVAL for
               other errors.  It can also fail with errors of Specifying
               messages.  Occurrence of some of the errors depend on the value
               of expandaddr.  Any error stops processing of further messages.

     Mail      (Compose mode) Similar to mail, but saves the message in a file
               named after the local part of the first recipient's address
               (instead of in record).

     mail      (Compose mode)(m) Takes a (list of) recipient address(es) as (an)
               argument(s), or asks on standard input if none were given; then
               collects the remaining mail content and sends it out.  Unless the
               internal variable fullnames is set recipient addresses will be
               stripped from comments, names etc.  For more documentation please
               refer to On sending mail, and non-interactive mode.

               This may generate the errors ^ERR-DESTADDRREQ if no receiver has
               been specified, ^ERR-PERM if some addressees where rejected by
               expandaddr, ^ERR-NOTSUP if multiple messages have been specified,
               ^ERR-IO if an I/O error occurs, ^ERR-NOTSUP if a necessary
               character set conversion fails, and ^ERR-INVAL for other errors.
               It can also fail with errors of Specifying messages.  Occurrence
               of some of the errors depend on the value of expandaddr.

     mailcap   [Option] When used without arguments or if show has been given
               the content of The Mailcap files cache is shown,
               (re-)initializing it first (as necessary.  If the argument is
               load then the cache will only be (re-)initialized, and clear will
               remove its contents.  Note that Mail will try to load the files
               only once, use ‘mailcap clear’ to unlock further attempts.
               Loading and parsing can be made more verbose.

     mbox      (mb) The given message list is to be sent to the secondary
               mailbox MBOX when Mail is quit; this is the default action unless
               the variable hold is set.  [v15 behaviour may differ] This
               command can only be used in a primary system mailbox.

     mimetype, unmimetype
               [Only new quoting rules] Without arguments the content of the
               MIME type cache will displayed; a more verbose listing will be
               produced if either of debug or verbose are set.  When given
               arguments they will be joined, interpreted as shown in The
               mime.types files (also see HTML mail and MIME attachments), and
               the resulting entry will be added (prepended) to the cache.  In
               any event MIME type sources are loaded first as necessary –
               mimetypes-load-control can be used to fine-tune which sources are
               actually loaded.

               The latter command deletes all specifications of the given MIME
               type, thus ‘? unmimetype text/plain’ will remove all registered
               specifications for the MIME type ‘text/plain’.  The special name
               ‘*’ will discard all existing MIME types, just as will ‘reset’,
               but which also reenables cache initialization via
               mimetypes-load-control.

     mimeview  [v15 behaviour may differ] Only available in interactive mode,
               this command allows execution of external MIME type handlers
               which do not integrate into the normal type output (see HTML mail
               and MIME attachments).  ([v15 behaviour may differ] No syntax to
               directly address parts, this restriction may vanish.)  The user
               will be asked for each non-text part of the given message in turn
               whether the registered handler shall be used to display the part.

     mlist, unmlist
               [Only new quoting rules] Manage the list of known Mailing lists;
               subscriptions are controlled via mlsubscribe.  The latter command
               deletes all given arguments, or all at once when given the
               asterisk ‘*’.  The former shows the list of all currently known
               lists if used without arguments, otherwise the given arguments
               will become known.  [Option] In the latter case, arguments which
               contain any of the magic regular expression characters will be
               interpreted as one, possibly matching many addresses; these will
               be sequentially matched via linked lists instead of being looked
               up in a dictionary.

     mlsubscribe, unmlsubscribe
               Building upon the command pair mlist, unmlist, but only managing
               the subscription attribute of mailing lists.  (The former will
               also create not yet existing mailing lists.)

     Move      Similar to move, but move the messages to a file named after the
               local part of the sender of the first message instead of taking a
               filename argument; outfolder is inspected to decide on the actual
               storage location.

     move      Acts like copy but marks the messages for deletion if they were
               transferred successfully.

     More      Like more, but also displays header fields which would not pass
               the headerpick selection, and all MIME parts.  Identical to Page.

     more      Invokes the PAGER on the given messages, even in non-interactive
               mode and as long as the standard output is a terminal.  Identical
               to page.

     mtaaliases
               [Option] When used without arguments or if show has been given
               the content of the mta-aliases cache is shown, (re-)initializing
               it first (as necessary).  If the argument is load then the cache
               will only be (re-)initialized, and clear will remove its
               contents.

     netrc     [Option] When used without arguments, or when the argument was
               show the content of the ~/.netrc cache is shown, initializing it
               as necessary.  If the argument is load then the cache will be
               (re)loaded, whereas clear removes it.  Loading and parsing can be
               made more verbose.  lookup will query the cache for the URL given
               as the second argument (‘[USER@]HOST’).  See netrc-lookup,
               netrc-pipe and the section On URL syntax and credential lookup;
               the section The .netrc file documents the file format in detail.

     newmail   Checks for new mail in the current folder without committing any
               changes before.  If new mail is present, a message is shown.  If
               the header variable is set, the headers of each new message are
               also shown.  This command is not available for all mailbox types.

     next      (n) (like ‘+’ or “ENTER”) Goes to the next message in sequence
               and types it.  With an argument list, types the next matching
               message.

     New       Same as Unread.

     new       Same as unread.

     noop      If the current folder is accessed via a network connection, a
               “NOOP” command is sent, otherwise no operation is performed.

     Page      Like page, but also displays header fields which would not pass
               the headerpick selection, and all MIME parts.  Identical to More.

     page      Invokes the PAGER on the given messages, even in non-interactive
               mode and as long as the standard output is a terminal.  Identical
               to more.

     Pipe      Like pipe but also pipes header fields which would not pass the
               headerpick selection, and all parts of MIME
               ‘multipart/alternative’ messages.

     pipe      (pi) Takes an optional message list and shell command (that
               defaults to cmd), and pipes the messages through the command.  If
               the page variable is set, every message is followed by a formfeed
               character.

     preserve  (pre) A synonym for hold.

     Print     (P) Alias for Type.

     print     (p) Research UNIX equivalent of type.

     quit      (q) Terminates the session, saving all undeleted, unsaved
               messages in the current secondary mailbox MBOX, preserving all
               messages marked with hold or preserve or never referenced in the
               system inbox, and removing all other messages from the primary
               system mailbox.  If new mail has arrived during the session, the
               message “You have new mail” will be shown.  If given while
               editing a mailbox file with the command line option -f, then the
               edit file is rewritten.  A return to the shell is effected,
               unless the rewrite of edit file fails, in which case the user can
               escape with the exit command.  The optional status number
               argument will be passed through to exit(3).  [v15 behaviour may
               differ] For now it can happen that the given status will be
               overwritten, later this will only occur if a later error needs to
               be reported onto an otherwise success indicating status.

     read      [Only new quoting rules] Read a line from standard input, or the
               channel set active via readctl, and assign the data, which will
               be split as indicated by ifs, to the given variables.  The
               variable names are checked by the same rules as documented for
               vput, and the same error codes will be seen in !; the exit status
               ? indicates the number of bytes read, it will be ‘-1’ with the
               error number ! set to ^ERR-BADF in case of I/O errors, or
               ^ERR-NONE upon End-Of-File.  If there are more fields than
               variables, assigns successive fields to the last given variable.
               If there are less fields than variables, assigns the empty string
               to the remains.

                     ? read a b c
                        H  e  l  l  o
                     ? echo "<$a> <$b> <$c>"
                     <H> <e> <l  l  o>
                     ? wysh set ifs=:; read a b c;unset ifs
                     hey2.0,:"'you    ",:world!:mars.:
                     ? echo $?/$^ERRNAME / <$a><$b><$c>
                     0/NONE / <hey2.0,><"'you    ",><world!:mars.:><><>

     readsh    [Only new quoting rules] Like read, but splits on shell token
               boundaries (see Shell-style argument quoting) rather than at ifs.
               [v15 behaviour may differ] Could become a commandalias, maybe
               ‘read --tokenize --’.

     readall   [Only new quoting rules] Read anything from standard input, or
               the channel set active via readctl, and assign the data to the
               given variable.  The variable name is checked by the same rules
               as documented for vput, and the same error codes will be seen in
               !; the exit status ? indicates the number of bytes read, it will
               be ‘-1’ with the error number ! set to ^ERR-BADF in case of I/O
               errors, or ^ERR-NONE upon End-Of-File.  [v15 behaviour may
               differ] The input data length is restricted to 31-bits.

     readctl   [Only new quoting rules] Manages input channels for read, readsh
               and readall, to be used to avoid complicated or impracticable
               code, like calling read from within a macro in non-interactive
               mode.  Without arguments, or when the first argument is show, a
               listing of all known channels is printed.  Channels can otherwise
               be created, and existing channels can be set active and removed
               by giving the string used for creation.

               The channel name is expected to be a file descriptor number, or,
               if parsing the numeric fails, an input file name that undergoes
               Filename transformations.  For example (this example requires a
               modern shell):

                     $ printf 'echon "hey, "\nread a\nyou\necho $a' |\
                       mail -R#
                     hey, you
                     $ LC_ALL=C printf 'echon "hey, "\nread a\necho $a' |\
                       LC_ALL=C 6<<< 'you' mail -R#X'readctl create 6'
                     hey, you

     remove    [Only new quoting rules] Removes the named files or directories.
               If a name refers to a mailbox, say a Maildir mailbox, then a
               mailbox type specific removal will be performed, deleting the
               complete mailbox.  In interactive mode the user is asked for
               confirmation.

     rename    [Only new quoting rules] Takes the name of an existing folder and
               the name for the new folder and renames the first to the second
               one.  Filename transformations including shell pathname wildcard
               pattern expansions (glob(7)) are performed on both arguments.
               Both folders must be of the same type.

     Reply, Respond
               (Compose mode)(R) Identical to reply except that it replies to
               only the sender of each message of the given list, by using the
               first message as the template to quote, for the ‘Subject:’ etc.;
               setting flipr will exchange this command with reply.

     reply, respond
               (Compose mode)(r) Take a message (list) and group-respond (to
               each in turn) by addressing the sender and all recipients,
               subject to fullnames and alternates processing.  followup-to,
               followup-to-honour, reply-to-honour as well as recipients-in-cc
               influence response behaviour.  quote as well as
               quote-as-attachment configure whether responded-to message shall
               be quoted etc., content-description-quote-attachment may be used.
               Setting flipr will exchange this command with Reply.  The command
               Lreply offers special support for replying to mailing lists.  For
               more documentation please refer to On sending mail, and non-
               interactive mode.

               This may generate the errors ^ERR-DESTADDRREQ if no receiver has
               been specified, or was rejected by expandaddr policy, ^ERR-IO if
               an I/O error occurs, ^ERR-NOTSUP if a necessary character set
               conversion fails, and ^ERR-INVAL for other errors.  It can also
               fail with errors of Specifying messages.  Any error stops
               processing of further messages.

     Resend    Like resend, but does not add any header lines.  This is not a
               way to hide the sender's identity, but useful for sending a
               message again to the same recipients.

     resend    Takes a list of messages and a name, and sends each message to
               the given addressee, which is subject to fullnames.
               ‘Resent-From:’ and related header fields are prepended to the new
               copy of the message.  Saving in record is only performed if
               record-resent is set.  [v15 behaviour may differ](Compose mode)
               is not entered, the only supported hooks are on-resend-enter and
               on-resend-cleanup.

               This may generate the errors ^ERR-DESTADDRREQ if no receiver has
               been specified, or was rejected by expandaddr policy, ^ERR-IO if
               an I/O error occurs, ^ERR-NOTSUP if a necessary character set
               conversion fails, and ^ERR-INVAL for other errors.  It can also
               fail with errors of Specifying messages.  Any error stops
               processing of further messages.

     retain    (ret) Superseded by the multiplexer headerpick.

     return    Only available inside of a defined macro or an account, this
               command returns control of execution to the outer scope.  The two
               optional parameters are positive decimal numbers and default to
               0: the first specifies the 32-bit return value (stored in ? [v15
               behaviour may differ] and later extended to 64-bit), the second
               the 32-bit error number (stored in !).  As documented for ? a
               non-0 exit status may cause the program to exit.

     Save      (S) Similar to save, but saves the messages in a file named after
               the local part of the sender of the first message instead of
               taking a filename argument; outfolder is inspected to decide on
               the actual storage location.

     save      (s) Takes a message list and a filename and appends each message
               in turn to the end of the file.  Filename transformations
               including shell pathname wildcard pattern expansions (glob(7)) is
               performed on the filename.  If no filename is given, the
               secondary mailbox MBOX is used.  The filename in quotes, followed
               by the generated character count is echoed on the user's
               terminal.  If editing a primary system mailbox the messages are
               marked for deletion.  To filter the saved header fields to the
               desired subset use the ‘save’ slot of the white- and blacklisting
               command headerpick.  Also see Copy.

     savediscard
               [Obsolete] Superseded by the multiplexer headerpick.

     saveignore
               [Obsolete] Superseded by the multiplexer headerpick.

     saveretain
               [Obsolete] Superseded by the multiplexer headerpick.

     search    Takes a message specification (list) and displays a header
               summary of all matching messages, as via headers.  This command
               is an alias of from.  Also see Specifying messages.

     seen      Takes a message list and marks all messages as having been read.

     set, unset
               (se, [Only new quoting rules] uns) The latter command will delete
               all given global variables, or only block-scope local ones if the
               local command modifier has been used.  The former, when used
               without arguments, will show all currently known variables, being
               more verbose if either of debug or verbose is set.  Remarks: this
               list mode will not automatically link-in known ENVIRONMENT
               variables, but only explicit addressing will do so, examples are
               varshow, using a variable in an if condition or a string passed
               to echo, explicit setting, as well as some program-internal use
               cases.

               Otherwise the given variables (and arguments) are set or
               adjusted.  Arguments are of the form ‘name=value’ (no space
               before or after ‘=’), or plain ‘name’ if there is no value, i.e.,
               a boolean variable.  If a name begins with ‘no’, as in ‘set
               nosave’, the effect is the same as invoking the unset command
               with the remaining part of the variable (‘unset save’).  [v15
               behaviour may differ] In conjunction with the wysh (or local)
               command prefix(es) Shell-style argument quoting can be used to
               quote arguments as necessary.  [v15 behaviour may differ]
               Otherwise quotation marks may be placed around any part of the
               assignment statement to quote blanks or tabs.

               When operating in global scope any ‘name’ that is known to map to
               an environment variable will automatically cause updates in the
               program environment (unsetting a variable in the environment
               requires corresponding system support) — use the command environ
               for further environmental control.  If the command modifier local
               has been used to alter the command to work in block-scope all
               variables have values (may they be empty), and creation of names
               which shadow INTERNAL VARIABLES is actively prevented ([v15
               behaviour may differ] shadowing of linked ENVIRONMENT variables
               and free-form versions of variable chains is not yet detected).
               Also see varshow and the sections INTERNAL VARIABLES and
               ENVIRONMENT.

                     ? wysh set indentprefix=' -> '
                     ? wysh set atab=$'' aspace=' ' zero=0

     shcodec   Apply shell quoting rules to the given raw-data arguments.
               Supports vput (see Command modifiers).  The first argument
               specifies the operation: [+]e[ncode] or d[ecode] cause shell
               quoting to be applied to the remains of the line, and expanded
               away thereof, respectively.  If the former is prefixed with a
               plus-sign, the quoted result will not be roundtrip enabled, and
               thus can be decoded only in the very same environment that was
               used to perform the encode; also see mle-quote-rndtrip.  If the
               coding operation fails the error number ! is set to
               ^ERR-CANCELED, and the unmodified input is used as the result;
               the error number may change again due to output or result storage
               errors.

     shell     [Only new quoting rules] (sh) Invokes an interactive version of
               the shell, and returns its exit status.

     shortcut, unshortcut
               [Only new quoting rules] Manage the file- or pathname shortcuts
               as documented for folder.  The latter command deletes all
               shortcuts given as arguments, or all at once when given the
               asterisk ‘*’.  The former shows the list of all currently defined
               shortcuts if used without arguments, the target of the given with
               a single argument.  Otherwise arguments are treated as pairs of
               shortcuts and their desired expansion, creating new or updating
               already existing ones.

     shift     [Only new quoting rules] Shift the positional parameter stack
               (starting at 1) by the given number (which must be a positive
               decimal), or 1 if no argument has been given.  It is an error if
               the value exceeds the number of positional parameters.  If the
               given number is 0, no action is performed, successfully.  The
               stack as such can be managed via vpospar.  Note this command will
               fail in account and hook macros unless the positional parameter
               stack has been explicitly created in the current context via
               vpospar.

     show      Like type, but performs neither MIME decoding nor decryption, so
               that the raw message text is shown.

     size      (si) Shows the size in characters of each message of the given
               message list.

     sleep     [Only new quoting rules] Sleep for the specified number of
               seconds (and optionally milliseconds), by default interruptible.
               If a third argument is given the sleep will be uninterruptible,
               otherwise the error number ! will be set to ^ERR-INTR if the
               sleep has been interrupted.  The command will fail and the error
               number will be ^ERR-OVERFLOW if the given duration(s) overflow
               the time datatype, and ^ERR-INVAL if the given durations are no
               valid integers.

     sort, unsort
               The latter command disables sorted or threaded mode, returns to
               normal message order and, if the header variable is set, displays
               a header summary.  The former command shows the current sorting
               criterion when used without an argument, but creates a sorted
               representation of the current folder otherwise, and changes the
               next command and the addressing modes such that they refer to
               messages in the sorted order.  Message numbers are the same as in
               regular mode.  If the header variable is set, a header summary in
               the new order is also displayed.  Automatic folder sorting can be
               enabled by setting the autosort variable, as in ‘set
               autosort=thread’.  Possible sorting criterions are:

               date     Sort the messages by their ‘Date:’ field, that is by the
                        time they were sent.
               from     Sort messages by the value of their ‘From:’ field, that
                        is by the address of the sender.  If the showname
                        variable is set, the sender's real name (if any) is
                        used.
               size     Sort the messages by their size.
               spam     [Option] Sort the message by their spam score, as has
                        been classified by spamrate.
               status   Sort the messages by their message status.
               subject  Sort the messages by their subject.
               thread   Create a threaded display.
               to       Sort messages by the value of their ‘To:’ field, that is
                        by the address of the recipient.  If the showname
                        variable is set, the recipient's real name (if any) is
                        used.

     source    [Only new quoting rules] (so) The source command reads commands
               from the given file.  Filename transformations will be applied.
               If the given expanded argument ends with a vertical bar ‘|’ then
               the argument will instead be interpreted as a shell command and
               Mail will read the output generated by it.  Dependent on the
               settings of posix and errexit, and also dependent on whether the
               command modifier ignerr had been used, encountering errors will
               stop sourcing of the given input.  [v15 behaviour may differ]
               Note that source cannot be used from within macros that execute
               as folder-hooks or accounts, i.e., it can only be called from
               macros that were called.

     source_if
               [Only new quoting rules] The difference to source (beside not
               supporting pipe syntax aka shell command input) is that this
               command will not generate an error nor warn if the given file
               argument cannot be opened successfully.

     spamclear
               [Option] Takes a list of messages and clears their ‘is-spam’
               flag.

     spamforget
               [Option] Takes a list of messages and causes the spam-interface
               to forget it has ever used them to train its Bayesian filter.
               Unless otherwise noted the ‘is-spam’ flag of the message is
               inspected to chose whether a message shall be forgotten to be
               “ham” or “spam”.

     spamham   [Option] Takes a list of messages and informs the Bayesian filter
               of the spam-interface that they are “ham”.  This also clears the
               ‘is-spam’ flag of the messages in question.

     spamrate  [Option] Takes a list of messages and rates them using the
               configured spam-interface, without modifying the messages, but
               setting their ‘is-spam’ flag as appropriate; because the spam
               rating headers are lost the rate will be forgotten once the
               mailbox is left.  Refer to the manual section Handling spam for
               the complete picture of spam handling in Mail.

     spamset   [Option] Takes a list of messages and sets their ‘is-spam’ flag.

     spamspam  [Option] Takes a list of messages and informs the Bayesian filter
               of the spam-interface that they are “spam”.  This also sets the
               ‘is-spam’ flag of the messages in question.

     thread    [Obsolete] The same as ‘sort thread’ (consider using a
               ‘commandalias’ as necessary).

     tls       [Only new quoting rules] TLS information and management command
               multiplexer to aid in Encrypted network communication, mostly
               available only if the term ‘+sockets’ is included in features.
               Commands support vput if so documented (see Command modifiers).
               The result that is shown in case of errors is always the empty
               string, errors can be identified via the error number !.  For
               example, string length overflows are caught and set ! to
               ^ERR-OVERFLOW.  The TLS configuration is honoured, especially
               tls-verify.

                     ? vput tls result fingerprint pop3s://ex.am.ple
                     ? echo $?/$!/$^ERRNAME: $result

               certchain Show the complete verified peer certificate chain.
                         Includes informational fields in conjunction with
                         verbose.

               certificate Show only the peer certificate, without any signers.
                         Includes informational fields in conjunction with
                         verbose.

               fingerprint Show the tls-fingerprint-digested fingerprint of the
                         certificate of the given HOST (‘server:port’, where the
                         port defaults to the HTTPS port, 443).  tls-fingerprint
                         is actively ignored for the runtime of this command.

     Top       Like top but always uses the headerpick ‘type’ slot for white-
               and blacklisting header fields.

     top       (to) Takes a message list and types out the first toplines lines
               of each message on the user's terminal.  Unless a special
               selection has been established for the ‘top’ slot of the
               headerpick command, the only header fields that are displayed are
               ‘From:’, ‘To:’, ‘Cc:’, and ‘Subject:’.  Top will always use the
               ‘type’ headerpick selection instead.  It is possible to apply
               compression to what is displayed by setting topsqueeze.  Messages
               are decrypted and converted to the terminal character set if
               necessary.

     touch     (tou) Takes a message list and marks the messages for saving in
               the secondary mailbox MBOX.  Mail deviates from the POSIX
               standard with this command, as a following next command will
               display the following message instead of the current one.

     Type      (T) Like type but also displays header fields which would not
               pass the headerpick selection, and all visualizable parts of MIME
               ‘multipart/alternative’ messages.

     type      (t) Takes a message list and types out each message on the user's
               terminal.  The display of message headers is selectable via
               headerpick.  For MIME multipart messages, all parts with a
               content type of ‘text’, all parts which have a registered MIME
               type handler (see HTML mail and MIME attachments) which produces
               plain text output, and all ‘message’ parts are shown, others are
               hidden except for their headers.  Messages are decrypted and
               converted to the terminal character set if necessary.  The
               command mimeview can be used to display parts which are not
               displayable as plain text.

     unaccount
               See account.

     unalias   (una) See alias.

     unanswered
               See answered.

     unbind    See bind.

     uncollapse
               See collapse.

     uncolour  See colour.

     undefine  See define.

     undelete  See delete.

     undraft   See draft.

     unflag    See flag.

     unfwdignore
               [Obsolete] Superseded by the multiplexer headerpick.

     unfwdretain
               [Obsolete] Superseded by the multiplexer headerpick.

     unignore  Superseded by the multiplexer headerpick.

     unmimetype
               See mimetype.

     unmlist   See mlist.

     unmlsubscribe
               See mlsubscribe.

     Unread    Same as unread.

     unread    Takes a message list and marks each message as not having been
               read.

     unretain  Superseded by the multiplexer headerpick.

     unsaveignore
               [Obsolete] Superseded by the multiplexer headerpick.

     unsaveretain
               [Obsolete] Superseded by the multiplexer headerpick.

     unset     [Only new quoting rules] (uns) See set.

     unshortcut
               See shortcut.

     unsort    See short.

     unthread  [Obsolete] Same as unsort.

     urlcodec  Perform URL percent codec operations on the raw-data argument,
               rather according to RFC 3986.  The first argument specifies the
               operation: e[ncode] or d[ecode] perform plain URL percent en- and
               decoding, respectively.  p[ath]enc[ode] and p[ath]dec[ode]
               perform a slightly modified operation which should be better for
               pathnames: it does not allow a tilde ‘~’, and will neither accept
               hyphen-minus ‘-’ nor dot ‘’.  as an initial character.  The
               remains of the line form the URL data which is to be converted.
               This is a character set agnostic operation, and it may thus
               decode bytes which are invalid in the current ttycharset.

               Supports vput (see Command modifiers), and manages the error
               number !.  If the coding operation fails the error number ! is
               set to ^ERR-CANCELED, and the unmodified input is used as the
               result; the error number may change again due to output or result
               storage errors.  [v15 behaviour may differ] This command does not
               know about URLs beside what is documented.  (vexpr offers a
               makeprint subcommand, shall the URL be displayed.)

     varshow   [Only new quoting rules] This command produces the same output as
               the listing mode of set, including verboseity adjustments, but
               only for the given variables.

     verify    [Option] Takes a message list and verifies each message.  If a
               message is not a S/MIME signed message, verification will fail
               for it.  The verification process checks if the message was
               signed using a valid certificate, if the message sender's email
               address matches one of those contained within the certificate,
               and if the message content has been altered.

     version   Shows the version and features of Mail, optionally in a more
               verbose form which also includes the build and running system
               environment.  This command supports vput (see Command modifiers).

     vexpr     [Only new quoting rules] A multiplexer command which offers
               signed 64-bit numeric calculations, as well as other, mostly
               string-based operations.  C-style byte string operations are
               available via csop.  The first argument defines the number, type,
               and meaning of the remaining arguments.  An empty number argument
               is treated as 0.  Supports vput (see Command modifiers).  The
               result shown in case of errors is ‘-1’ for usage errors and
               numeric operations, the empty string otherwise; “soft” errors,
               like when a search operation failed, will also set the ! error
               number to ^ERR-NODATA.  Except when otherwise noted numeric
               arguments are parsed as signed 64-bit numbers, and errors will be
               reported in the error number ! as the numeric error ^ERR-RANGE.

               Numeric operations work on one or two signed 64-bit integers.
               Numbers prefixed with ‘0x’ or ‘0X’ are interpreted as hexadecimal
               (base 16) numbers, whereas ‘0’ indicates octal (base 8), and ‘0b’
               as well as ‘0B’ denote binary (base 2) numbers.  It is possible
               to use any base in between 2 and 36, inclusive, with the
               ‘BASE#number’ notation, where the base is given as an unsigned
               decimal number, so ‘16#AFFE’ is a different way of specifying a
               hexadecimal number.  Unsigned interpretation of a number can be
               enforced by prefixing an ‘u’ (case-insensitively), as in ‘u-110’;
               this is not necessary for power-of-two bases (2, 4, 8, 16 and
               32), which will be interpreted as unsigned by default, but it
               still makes a difference regarding overflow detection and
               overflow constant.  It is possible to enforce signed
               interpretation by (instead) prefixing a ‘s’ (case-insensitively).
               The number sign notation uses a permissive parse mode and as such
               supports complicated conditions out of the box:

                     ? wysh set ifs=:;read i;unset ifs;echo $i;vexpr pb 2 10#$i
                        -009
                     <   -009>
                     0b1001

               One integer is expected by assignment (equals sign ‘=’), which
               does nothing but parsing the argument, thus detecting validity
               and possible overflow conditions, unary not (tilde ‘~’), which
               creates the bitwise complement, and unary plus and minus.  Two
               integers are used by addition (plus sign ‘+’), subtraction
               (hyphen-minus ‘-’), multiplication (asterisk ‘*’), division
               (solidus ‘/’) and modulo (percent sign ‘%’), as well as for the
               bitwise operators logical or (vertical bar ‘|’, to be quoted) ,
               bitwise and (ampersand ‘&’, to be quoted) , bitwise xor
               (circumflex ‘^’), the bitwise signed left- and right shifts
               (‘<<’, ‘>>’), as well as for the unsigned right shift ‘>>>’.

               Another numeric operation is pbase, which takes a number base in
               between 2 and 36, inclusive, and will act on the second number
               given just the same as what equals sign ‘=’ does, but the number
               result will be formatted in the base given, as a signed 64-bit
               number unless unsigned interpretation of the input number had
               been forced (with an u prefix).

               Numeric operations support a saturated mode via the question mark
               ‘?’ modifier suffix; the keyword ‘saturated’ is optional, ‘+?’,
               ‘+?satu’, and ‘+?saturated’ are therefore identical.  In
               saturated mode overflow errors and division and modulo by zero
               are no longer reported via the exit status, but the result will
               linger at the minimum or maximum possible value, instead of
               overflowing (or trapping).  This is true also for the argument
               parse step.  For the bitwise shifts, the saturated maximum is 63.
               Any caught overflow will be reported via the error number ! as
               ^ERR-OVERFLOW.

                     ? vput vexpr res -? +1 -9223372036854775808
                     ? echo $?/$!/$^ERRNAME:$res
                     0/75/OVERFLOW:-9223372036854775808

               Character set agnostic string functions have no notion of locale
               settings and character sets.

               date-utc  Outputs the current date and time in UTC (Coordinated
                         Universal Time) with values named such that ‘vput vexpr
                         x date-utc; eval wysh set $x’ creates accessible
                         variables.

               date-stamp-utc Outputs a RFC 3339 internet date/time format of
                         UTC.

               epoch     The seconds and nanoseconds since the Unix epoch
                         (1970-01-01T00:00:00) named ‘epoch_sec’ and
                         ‘epoch_nsec’ such that ‘vput vexpr x epoch; eval wysh
                         set $x’ creates accessible variables.

               file-expand Performs the usual Filename transformations on its
                         argument.

               file-stat, file-lstat Perform the usual Filename transformations
                         on the argument, then call stat(2) and lstat(2),
                         respectively, and output values such that ‘vput vexpr x
                         file-stat FILE; eval wysh set $x’ creates accessible
                         variables.  The variable ‘st_type’ uses solidus ‘/’ to
                         denote directories, commercial at ‘@’ for links, number
                         sign ‘#’ for block devices, percent sign ‘%’ for for
                         character devices, vertical bar ‘|’ for FIFOs, equal
                         sign ‘=’ for sockets, and the period ‘.’ for the rest.

               random    Generates a random string of the given length, or of
                         PATH_MAX bytes (a constant from /usr/include) if the
                         value 0 is given; the random string will be base64url
                         encoded according to RFC 4648, and thus be usable as a
                         (portable) filename.

               String operations work, sufficient support provided, according to
               the active user's locale encoding and character set (see
               Character sets).  Where the question mark ‘?’ modifier suffix is
               supported, a case-insensitive operation mode is available; the
               keyword ‘case’ is optional, ‘regex?’ and ‘regex?case’ are
               therefore identical.

               makeprint (One-way) Converts the argument to something safely
                         printable on the terminal.

               regex     [Option] A string operation that will try to match the
                         first argument with the regular expression given as the
                         second argument.  ‘?’ modifier suffix is supported.  If
                         the optional third argument has been given then instead
                         of showing the match offset a replacement operation is
                         performed: the third argument is treated as if
                         specified within dollar-single-quote (see Shell-style
                         argument quoting), and any occurrence of a positional
                         parameter, for example 0, 1 etc. is replaced with the
                         according match group of the regular expression:

                               ? vput vexpr res regex bananarama \
                                   (.*)NanA(.*) '\${1}au\$2'
                               ? echo $?/$!/$^ERRNAME:$res:
                               1/61/NODATA::
                               ? vput vexpr res regex?case bananarama \
                                   (.*)NanA(.*) '\${1}uauf\$2'
                               ? echo $?/$!/$^ERRNAME:$res:
                               0/0/NONE:bauauframa:

     vpospar   [Only new quoting rules] Manage the positional parameter stack
               (see 1, #, *, @ as well as shift).  If the first argument is
               ‘clear’, then the positional parameter stack of the current
               context, or the global one, if there is none, is cleared.  If it
               is ‘set’, then the remaining arguments will be used to (re)create
               the stack, if the parameter stack size limit is excessed an
               ^ERR-OVERFLOW error will occur.

               If the first argument is ‘quote’, a round-trip capable
               representation of the stack contents is created, with each quoted
               parameter separated from each other with the first character of
               ifs, and followed by the first character of if-ws, if that is not
               empty and not identical to the first.  If that results in no
               separation at all a space character is used.  This mode supports
               vput (see Command modifiers).  I.e., the subcommands ‘set’ and
               ‘quote’ can be used (in conjunction with eval) to (re)create an
               argument stack from and to a single variable losslessly.

                     ? vpospar set hey, "'you    ", world!
                     ? echo $#: <${1}><${2}><${3}>
                     ? vput vpospar x quote
                     ? vpospar clear
                     ? echo $#: <${1}><${2}><${3}>
                     ? eval vpospar set ${x}
                     ? echo $#: <${1}><${2}><${3}>

     visual    (v) Takes a message list and invokes the VISUAL display editor on
               each message.  Modified contents are discarded unless the
               writebackedited variable is set, and are not used unless the
               mailbox can be written to and the editor returns a successful
               exit status.  edit can be used instead for a less display
               oriented editor.

     write     (w) For conventional messages the body without all headers is
               written.  The original message is never marked for deletion in
               the originating mail folder.  The output is decrypted and
               converted to its native format as necessary.  If the output file
               exists, the text is appended.  If a message is in MIME multipart
               format its first part is written to the specified file as for
               conventional messages, handling of the remains depends on the
               execution mode.  No special handling of compressed files is
               performed.

               In interactive mode the user is consecutively asked for the
               filenames of the processed parts.  For convenience saving of each
               part may be skipped by giving an empty value, the same result as
               writing it to /dev/null.  Shell piping the part content by
               specifying a leading vertical bar ‘|’ character for the filename
               is supported.  Other user input undergoes the usual Filename
               transformations, including shell pathname wildcard pattern
               expansions (glob(7)) and shell variable expansion for the message
               as such, not the individual parts, and contents of the
               destination file are overwritten if the file previously existed.
               Character set conversion to ttycharset is performed when saving
               text data.

               [v15 behaviour may differ] In non-interactive mode any part which
               does not specify a filename is ignored, and suspicious parts of
               filenames of the remaining parts are URL percent encoded (as via
               urlcodec) to prevent injection of malicious character sequences,
               resulting in a filename that will be written into the current
               directory.  Existing files will not be overwritten, instead the
               part number or a dot are appended after a number sign ‘#’ to the
               name until file creation succeeds (or fails due to other
               reasons).

     xcall     [Only new quoting rules] The sole difference to call is that the
               new macro is executed in place of the current one, which will not
               regain control: all resources of the current macro will be
               released first.  This implies that any setting covered by
               localopts will be forgotten and covered variables will become
               cleaned up.  If this command is not used from within a called
               macro it will silently be (a more expensive variant of) call.

     xit       (x) A synonym for exit.

     z         [Only new quoting rules] Mail presents message headers in
               screenfuls as described under the headers command.  Without
               arguments this command scrolls to the next window of messages,
               likewise if the argument is ‘+’.  An argument of ‘-’ scrolls to
               the last, ‘^’ scrolls to the first, and ‘$’ to the last screen of
               messages.  A number argument prefixed by ‘+’ or ‘-’ indicates
               that the window is calculated in relation to the current
               position, and a number without a prefix specifies an absolute
               position.

     Z         [Only new quoting rules] Similar to z, but scrolls to the next or
               previous window that contains at least one ‘new’ or flagged
               message.

COMMAND ESCAPES
     When composing messages command escapes are available in interactive mode,
     when explicitly requested via -~, as well as in batch mode (-#).  They
     perform special functions, like editing headers of the message being
     composed, calling normal COMMANDS, yielding a shell, etc.  Command escapes
     are only recognized at the beginning of lines, and consist of an escape
     followed by a command character.  The default escape character is the tilde
     ‘~’.

     Unless otherwise documented command escapes ensure proper updates of the
     error number ! and the exit status ?.  The variable errexit controls
     whether a failed operation errors out message compose mode and causes
     program exit.  Escapes may be prefixed by none to multiple single character
     command modifiers, interspersed whitespace is ignored:

     An effect equivalent to the command modifier ignerr can be achieved
         with hyphen-minus ‘-’, overriding errexit.

     The modifier dollar ‘$’ evaluates the remains of the line; also see
         Shell-style argument quoting.  [v15 behaviour may differ] For now the
         entire input line is evaluated as a whole; to avoid that control
         operators like semicolon ; are interpreted unintentionally, they must
         be quoted.

     Addition of the command line to the [Option]al history can be prevented by
     placing whitespace directly after escape.  The [Option]al key bindings
     support a compose mode specific context.  The following command escapes are
     supported:

     ~~ string
               Insert the string of text in the message prefaced by a single
               ‘~’.  (If the escape character has been changed, that character
               must be doubled instead.)

     ~! command
               Execute the indicated shell command which follows, replacing
               unescaped exclamation marks with the previously executed command
               if the internal variable bang is set, then return to the message.

     ~.        End compose mode and send the message.  The hooks
               on-compose-splice-shell and on-compose-splice, in order, will be
               called when set, after which, in interactive mode askatend
               (leading to askcc, askbcc) and askattach will be checked as well
               as asksend, after which a set on-compose-leave hook will be
               called, autocc and autobcc will be joined in if set, finally a
               given message-inject-tail will be incorporated, after which the
               compose mode is left.

     ~: Mail-command or ~_ Mail-command
               Can be used to execute COMMANDS (which are allowed in compose
               mode).

     ~< filename
               Identical to ~r.

     ~<! command
               command is executed using the shell.  Its standard output is
               inserted into the message.

     ~?        [Option] Write a summary of command escapes.

     ~@ [filename...]
               Append or edit the list of attachments.  Does not manage the
               error number ! and the exit status ? (please use ~^ if error
               handling is necessary).  The append mode expects a list of
               filename arguments as shell tokens (see Shell-style argument
               quoting; token-separating commas are ignored, too), to be
               interpreted as documented for the command line option -a, with
               the message number exception as below.

               Without filename arguments the attachment list is edited, entry
               by entry; if a filename is left empty, that attachment is deleted
               from the list; once the end of the list is reached either new
               attachments may be entered or the session can be quit by
               committing an empty “new” attachment.  In non-interactive mode or
               in batch mode (-#) the list of attachments is effectively not
               edited but instead recreated; again, an empty input ends list
               creation.

               For all modes, if a given filename solely consists of the number
               sign ‘#’ followed by either a valid message number of the
               currently active mailbox, or by a period ‘.’, referring to the
               current message of the active mailbox, the so-called “dot”, then
               the given message is attached as a ‘message/rfc822’ MIME message
               part.  The number sign must be quoted to avoid misinterpretation
               as a shell comment character.

     ~| command
               Pipe the message text through the specified filter command.  If
               the command gives no output or terminates abnormally, retain the
               original text of the message.  The command fmt(1) is often used
               as a rejustifying filter.

               If the first character of the command is a vertical bar, then the
               entire message including header fields is subject to the filter
               command, so ‘~|| echo Fcc: /tmp/test; cat’ will prepend a file-
               carbon-copy message header.  Also see ~e, ~v.

     ~^ cmd [subcmd [arg3 [arg4]]]
               Low-level compose mode command which shares semantics with
               digmsg, and therefore evaluates its command line as documented in
               Shell-style argument quoting.  Does not manage the error number !
               and the exit status ?: errors are handled via the protocol, and
               hard errors like I/O failures cannot be handled.

               The protocol consists of command lines followed by (a) response
               line(s).  The first field of the response line represents a
               status code which specifies whether a command was successful or
               not, whether result data is to be expected, and if, the format of
               the result data.  Response data will be shell quoted as necessary
               for consumption by readsh, or eval and vpospar, to name a few.
               Error status code lines may optionally contain additional
               context:

               ‘210’     Status ok; the remains of the line are the result.
               ‘211’     Status ok; the rest of the line is optionally used for
                         more status.  What follows are lines of result
                         addresses, terminated by an empty line.  All the input,
                         including the empty line, must be consumed before
                         further commands can be issued.  Address lines consist
                         of two token, first the plain network address, e.g.,
                         ‘bob@exam.ple’, followed by the (quoted) full address
                         as known: ‘'(Lovely) Bob <bob@exam.ple>'’.  Non-network
                         addresses use the first field to indicate the type
                         (hyphen-minus ‘-’ for files, vertical bar ‘|’ for
                         pipes, and number sign ‘#’ for names which will undergo
                         alias processing) instead, the actual value will be in
                         the second field.
               ‘212’     Status ok; the rest of the line is optionally used for
                         more status.  What follows are lines of furtherly
                         unspecified (quoted) string content, terminated by an
                         empty line.  All the input, including the empty line,
                         must be consumed before further commands can be issued.
               ‘500’     Syntax error; invalid command.
               ‘501’     Syntax error in parameters or arguments.
               ‘505’     Error: an argument fails verification.  For example an
                         invalid address has been specified (also see
                         expandaddr), or an attempt was made to modify anything
                         in Mail's own namespace, or a modifying subcommand has
                         been used on a read-only message.
               ‘506’     Error: an otherwise valid argument is rendered invalid
                         due to context.  For example, a second address is added
                         to a header which may consist of a single address only.

               If a command indicates failure then the message will have
               remained unmodified.  Most commands can fail with ‘500’ if
               required arguments are missing, or excessive arguments have been
               given (false command usage).  ([v15 behaviour may differ] The
               latter does not yet occur regulary, because as stated in
               Shell-style argument quoting our argument parser is not yet smart
               enough to work on subcommand base; for example one might get
               excess argument error for a three argument subcommand that
               receives four arguments, but not for a four argument subcommand
               which receives six arguments: here excess will be joined.)  The
               following (case-insensitive) commands are supported:

               attachment This command allows listing, removal and addition of
                        message attachments.  The second argument specifies the
                        subcommand to apply, one of:

                        attribute This uses the same search mechanism as
                                  described for remove and prints any known
                                  attributes of the first found attachment via
                                  ‘212’ upon success or ‘501’ if no such
                                  attachment can be found.  The attributes are
                                  written as lines with a keyword and a value
                                  token.

                        attribute-at This uses the same search mechanism as
                                  described for remove-at and is otherwise
                                  identical to attribute.

                        attribute-set This uses the same search mechanism as
                                  described for remove, and will set the
                                  attribute given as the fourth to the value
                                  given as the fifth token argument.  If the
                                  value is an empty token, then the given
                                  attribute is removed, or reset to a default
                                  value if existence of the attribute is
                                  crucial.

                                  It returns via ‘210’ upon success, with the
                                  index of the found attachment following, ‘505’
                                  for message attachments or if the given
                                  keyword is invalid, and ‘501’ if no such
                                  attachment can be found.  The following
                                  keywords may be used (case-insensitively):

                                  ‘filename’  Sets the filename of the MIME
                                              part, i.e., the name that is used
                                              for display and when (suggesting a
                                              name for) saving (purposes).
                                  ‘content-description’ Associate some
                                              descriptive information to the
                                              attachment's content, used in
                                              favour of the plain filename by
                                              some MUAs.
                                  ‘content-id’ May be used for uniquely
                                              identifying MIME entities in
                                              several contexts; this expects a
                                              special reference address format
                                              as defined in RFC 2045 and
                                              generates a ‘505’ upon address
                                              content verification failure.
                                  ‘content-type’ Defines the media type/subtype
                                              of the part, which is managed
                                              automatically, but can be
                                              overwritten.
                                  ‘content-disposition’ Automatically set to the
                                              string ‘attachment’.

                        attribute-set-at This uses the same search mechanism as
                                  described for remove-at and is otherwise
                                  identical to attribute-set.

                        insert    Adds the attachment given as the third
                                  argument, specified exactly as documented for
                                  the command line option -a, and supporting the
                                  message number extension as documented for ~@.
                                  This reports ‘210’ upon success, with the
                                  index of the new attachment following, ‘505’
                                  if the given file cannot be opened, ‘506’ if
                                  an on-the-fly performed character set
                                  conversion fails, otherwise ‘501’ is reported;
                                  this is also reported if character set
                                  conversion is requested but not available.

                        list      List all attachments via ‘212’, or report
                                  ‘501’ if no attachments exist.  This command
                                  is the default command of attachment if no
                                  second argument has been given.

                        remove    This will remove the attachment given as the
                                  third argument, and report ‘210’ upon success
                                  or ‘501’ if no such attachment can be found.
                                  If there exists any path component in the
                                  given argument, then an exact match of the
                                  path which has been used to create the
                                  attachment is used directly, but if only the
                                  basename of that path matches then all
                                  attachments are traversed to find an exact
                                  match first, and the removal occurs
                                  afterwards; if multiple basenames match, a
                                  ‘506’ error occurs.  Message attachments are
                                  treated as absolute pathnames.

                                  If no path component exists in the given
                                  argument, then all attachments will be
                                  searched for ‘filename=’ parameter matches as
                                  well as for matches of the basename of the
                                  path which has been used when the attachment
                                  has been created; multiple matches result in a
                                  ‘506’.

                        remove-at This will interpret the third argument as a
                                  number and remove the attachment at that list
                                  position (counting from one!), reporting ‘210’
                                  upon success or ‘505’ if the argument is not a
                                  number or ‘501’ if no such attachment exists.

               header   This command allows listing, inspection, and editing of
                        message headers.  Header name case is not normalized, so
                        that case-insensitive comparison should be used when
                        matching names.  The second argument specifies the
                        subcommand to apply, one of:

                        insert    Create a new or an additional instance of the
                                  header given in the third argument, with the
                                  header body content as given in the fourth
                                  token.  It may return ‘501’ if the third
                                  argument specifies a free-form header field
                                  name that is invalid, or if body content
                                  extraction fails to succeed, ‘505’ if any
                                  extracted address does not pass syntax and/or
                                  security checks or on Mail namespace
                                  violations, and ‘506’ to indicate prevention
                                  of excessing a single-instance header — note
                                  that ‘Subject:’ can be appended to (a space
                                  separator will be added automatically first).
                                  ‘To:’, ‘Cc:’ and ‘Bcc:’ support the ‘?single’
                                  modifier to enforce treatment as a single
                                  addressee, for example ‘header insert
                                  To?single: 'exa, <m@ple>'’; the word ‘single’
                                  is optional.

                                  ‘210’ is returned upon success, followed by
                                  the name of the header and the list position
                                  of the newly inserted instance.  The list
                                  position is always 1 for single-instance
                                  header fields.  All free-form header fields
                                  are managed in a single list.

                        list      Without a third argument a list of all yet
                                  existing headers is given via ‘210’; this
                                  command is the default command of header if no
                                  second argument has been given.  A third
                                  argument restricts output to the given header
                                  only, which may fail with ‘501’ if no such
                                  field is defined.

                        remove    This will remove all instances of the header
                                  given as the third argument, reporting ‘210’
                                  upon success, ‘501’ if no such header can be
                                  found, and ‘505’ on Mail namespace violations.

                        remove-at This will remove from the header given as the
                                  third argument the instance at the list
                                  position (counting from one!) given with the
                                  fourth argument, reporting ‘210’ upon success
                                  or ‘505’ if the list position argument is not
                                  a number or on Mail namespace violations, and
                                  ‘501’ if no such header instance exists.

                        show      Shows the content of the header given as the
                                  third argument.  Dependent on the header type
                                  this may respond with ‘211’ or ‘212’; any
                                  failure results in ‘501’.

                        In compose-mode read-only access to optional pseudo
                        headers in the Mail private namespace is available:

                        ‘Mailx-Command:’
                                  The name of the command that generates the
                                  message, one of ‘forward’, ‘Lreply’, ‘mail’,
                                  ‘Reply’, ‘reply’, ‘resend’.  This pseudo
                                  header always exists (in compose-mode).
                        ‘Mailx-Raw-To:’
                        ‘Mailx-Raw-Cc:’
                        ‘Mailx-Raw-Bcc:’
                                  Represent the frozen initial state of these
                                  headers before any transformation (alias,
                                  alternates, recipients-in-cc etc.) took place.
                        ‘Mailx-Orig-Sender:’
                        ‘Mailx-Orig-From:’
                        ‘Mailx-Orig-To:’
                        ‘Mailx-Orig-Cc:’
                        ‘Mailx-Orig-Bcc:’
                                  The values of said headers of the original
                                  message which has been addressed by any of
                                  reply, forward, resend.  The sender field is
                                  special as it is filled in with the sole
                                  sender according to RFC 5322 rules, it may
                                  thus be equal to the from field.

               help, ?  Show an abstract of the above commands via ‘211’.

               version  This command will print the protocol version via ‘210’.

     ~A        The same as ‘~i Sign’.

     ~a        The same as ‘~i sign’.

     ~b name ...
               Add the given names to the list of blind carbon copy recipients.

     ~c name ...
               Add the given names to the list of carbon copy recipients.

     ~d        Read the file specified by the DEAD variable into the message.

     ~e        Invoke the text EDITOR on the message collected so far, then
               return to compose mode.  ~v can be used for a more display
               oriented editor, and ~|| offers a pipe-based editing approach.

     ~F messages
               Read the named messages into the message being sent, including
               all message headers and MIME parts, and honouring forward-add-cc
               as well as forward-inject-head and forward-inject-tail.  If no
               messages are specified, read in the current message, the “dot”.

     ~f messages
               Read the named messages into the message being sent.  If no
               messages are specified, read in the current message, the “dot”.
               Strips down the list of header fields according to the ‘forward’
               (with posix: ‘type’) white- and blacklist selection of
               headerpick, and honours forward-add-cc as well as
               forward-inject-head and forward-inject-tail.  For MIME multipart
               messages, only the first displayable part is included.

     ~H        In interactive mode, edit the message header fields ‘From:’,
               ‘Reply-To:’ and ‘Sender:’ by typing each one in turn and allowing
               the user to edit the field.  The default values for these fields
               originate from the from, reply-to and sender variables.  In non-
               interactive mode this sets ^ERR-NOTTY.

     ~h        In interactive mode, edit the message header fields ‘To:’, ‘Cc:’,
               ‘Bcc:’ and ‘Subject:’ by typing each one in turn and allowing the
               user to edit the field.  In non-interactive mode this sets
               ^ERR-NOTTY.

     ~I variable
               Insert the value of the specified variable into the message.  The
               message remains unaltered if the variable is unset or empty.  Any
               embedded character sequences ‘\t’ horizontal tabulator and ‘\n’
               line feed are expanded in posix mode; otherwise the expansion
               should occur at set time ([v15 behaviour may differ] by using the
               command modifier wysh).

     ~i variable
               Like ~I, but appends a newline character.

     ~M messages
               Read the named messages into the message being sent, indented by
               indentprefix.  If no messages are specified, read the current
               message, the “dot”.  Honours forward-add-cc as well as
               forward-inject-head and forward-inject-tail.

     ~m messages
               Read the named messages into the message being sent, indented by
               indentprefix.  If no messages are specified, read the current
               message, the “dot”.  Strips down the list of header fields
               according to the ‘type’ white- and blacklist selection of
               headerpick.  Honours forward-add-cc as well as
               forward-inject-head and forward-inject-tail.  For MIME multipart
               messages, only the first displayable part is included.

     ~p        Display the message collected so far, prefaced by the message
               header fields and followed by the attachment list, if any.

     ~Q        Read in the given / current message(s) using the algorithm of
               quote (except that is implicitly assumed, even if not set),
               honouring quote-add-cc.

     ~q        Abort the message being sent, copying it to the file specified by
               the DEAD variable if save is set.

     ~R filename
               Identical to ~r, but indent each line that has been read by
               indentprefix.

     ~r filename [HERE-delimiter]
               Read the named file, object to Filename transformations excluding
               shell globs and variable expansions, into the message; if
               filename is the hyphen-minus ‘-’ then standard input is used (for
               pasting, for example).  Only in this latter mode HERE-delimiter
               may be given: if it is data will be read in until the given
               HERE-delimiter is seen on a line by itself, and encountering EOF
               is an error; the HERE-delimiter is a required argument in non-
               interactive mode; if it is single-quote quoted then the pasted
               content will not be expanded, [v15 behaviour may differ]
               otherwise a future version of Mail may perform shell-style
               expansion on the content.

     ~s string
               Cause the named string to become the current subject field.
               Newline (NL) and carriage-return (CR) bytes are invalid and will
               be normalized to space (SP) characters.

     ~t name ...
               Add the given name(s) to the direct recipient list.

     ~U messages
               Read in the given / current message(s) excluding all headers,
               indented by indentprefix.  Honours forward-add-cc as well as
               forward-inject-head and forward-inject-tail.

     ~u messages
               Read in the given / current message(s), excluding all headers.
               Honours forward-add-cc as well as forward-inject-head and
               forward-inject-tail.

     ~v        Invoke the VISUAL editor on the message collected so far, then
               return to compose mode.  ~e can be used for a less display
               oriented editor, and ~|| offers a pipe-based editing approach.

     ~w filename
               Write the message onto the named file, which is object to the
               usual Filename transformations.  If the file exists, the message
               is appended to it.

     ~x        Same as ~q, except that the message is not saved at all.

INTERNAL VARIABLES
     Internal Mail variables are controlled via the set and unset commands;
     prefixing a variable name with the string ‘no’ and calling set has the same
     effect as using unset: ‘unset crt’ and ‘set nocrt’ do the same thing.
     varshow will give more insight on the given variable(s), and set, when
     called without arguments, will show a listing of all variables.  Both
     commands support a more verbose listing mode.  Some well-known variables
     will also become inherited from the program ENVIRONMENT implicitly, others
     can be imported explicitly with the command environ and henceforth share
     said properties.

     Two different kinds of internal variables exist, and both of which can also
     form chains.  There are boolean variables, which can only be in one of the
     two states “set” and “unset”, and value variables with a(n optional) string
     value.  For the latter proper quoting is necessary upon assignment time,
     the introduction of the section COMMANDS documents the supported quoting
     rules.

           ? wysh set one=val\ 1 two="val 2" \
               three='val "3"' four=$'val \'4\''; \
               varshow one two three four; \
               unset one two three four

     Dependent upon the actual option string values may become interpreted as
     colour names, command specifications, normal text, etc.  They may be
     treated as numbers, in which case decimal values are expected if so
     documented, but otherwise any numeric format and base that is valid and
     understood by the vexpr command may be used, too.

     There also exists a special kind of string value, the “boolean string”,
     which must either be a decimal integer (in which case ‘0’ is false and ‘1’
     and any other value is true) or any of the (case-insensitive) strings
     ‘off’, ‘no’, ‘n’ and ‘false’ for a false boolean and ‘on’, ‘yes’, ‘y’ and
     ‘true’ for a true boolean; a special kind of boolean string is the
     “quadoption”: it can optionally be prefixed with the (case-insensitive)
     term ‘ask-’, as in ‘ask-yes’; in interactive mode the user will be
     prompted, otherwise the actual boolean is used.

     Variable chains extend a plain ‘variable’ with ‘variable-HOST’ and
     ‘variable-USER@HOST’ variants.  Here ‘HOST’ will be converted to all
     lowercase when looked up (but not when the variable is set or unset!),
     [Option]ally IDNA converted, and indeed means ‘server:port’ if a ‘port’ had
     been specified in the contextual Uniform Resource Locator URL, see On URL
     syntax and credential lookup.  Even though this mechanism is based on URLs
     no URL percent encoding may be applied to neither of ‘USER’ nor ‘HOST’,
     variable chains need to be specified using raw data; the mentioned section
     contains examples.  Variables which support chains are explicitly
     documented as such, and Mail treats the base name of any such variable
     special, meaning that users should not create custom names like
     ‘variable-xyz’ in order to avoid false classifications and treatment of
     such variables.

   Initial settings
     The standard POSIX 2008/Cor 2-2016 mandates the following initial variable
     settings: noallnet, noappend, asksub, noaskbcc, noautoprint, nobang, nocmd,
     nocrt, nodebug, nodot, escape set to ‘~’, noflipr, nofolder, header,
     nohold, noignore, noignoreeof, nokeep, nokeepsave, nometoo, nooutfolder,
     nopage, prompt set to ‘? ’, noquiet, norecord, save, nosendwait, noshowto,
     noSign, nosign, toplines set to ‘5’.

     However, Mail has built-in some initial (and some default) settings which
     (may) diverge, others may become adjusted by one of the Resource files.
     Displaying the former is accomplished via set: ‘$ mail -:/ -v -Xset -Xx’.
     In general this implementation sets (and has extended the meaning of)
     sendwait, and does not support the noonehop variable – use command line
     options or mta-arguments to pass options through to a mta.  The default
     global resource file sets, among others, the variables hold, keep and
     keepsave, establishes a default headerpick selection etc., and should thus
     be taken into account.

   Variables
     ?         (Read-only) The exit status of the last command, or the return
               value of the macro called last.  This status has a meaning in the
               state machine: in conjunction with errexit any non-0 exit status
               will cause a program exit, and in posix mode any error while
               loading (any of the) resource files will have the same effect.
               ignerr, one of the Command modifiers, can be used to instruct the
               state machine to ignore errors.

     !         (Read-only) The current error number (errno(3)), which is set
               after an error occurred; it is also available via ^ERR, and the
               error name and documentation string can be queried via ^ERRNAME
               and ^ERRDOC.  [v15 behaviour may differ] This machinery is new
               and the error number is only really usable if a command
               explicitly states that it manages the variable !, for others
               errno will be used in case of errors, or ^ERR-INVAL if that is 0:
               it thus may or may not reflect the real error.  The error number
               may be set with the command return.

     ^         (Read-only) This is a multiplexer variable which performs dynamic
               expansion of the requested state or condition, of which there
               are:

               ^ERR, ^ERRDOC, ^ERRNAME
                         The number, documentation, and name of the current
                         errno(3), respectively, which is usually set after an
                         error occurred.  The documentation is an [Option], the
                         name is used if not available.  [v15 behaviour may
                         differ] This machinery is new and is usually reliable
                         only if a command explicitly states that it manages the
                         variable !, which is effectively identical to ^ERR.
                         Each of those variables can be suffixed with a hyphen
                         minus followed by a name or number, in which case the
                         expansion refers to the given error.  Note this is a
                         direct mapping of (a subset of) the system error
                         values:

                               define work {
                                 eval echo \$1: \$^ERR-$1:\
                                   \$^ERRNAME-$1: \$^ERRDOC-$1
                                 vput vexpr i + "$1" 1
                                 if [ $i -lt 16 ]
                                   \xcall work $i
                                 end
                               }
                               call work 0

               ^ERRQUEUE-COUNT, ^ERRQUEUE-EXISTS
                         The number of messages present in the [Option]al log
                         queue of errors, and a boolean which indicates whether
                         the queue is not empty, respectively; both are always 0
                         unless features indicates ‘+errors’.

     *         (Read-only) Expands all positional parameters (see 1), separated
               by the first character of the value of ifs.  [v15 behaviour may
               differ] The special semantics of the equally named special
               parameter of the sh(1) are not yet supported.

     @         (Read-only) Expands all positional parameters (see 1), separated
               by a space character.  If placed in double quotation marks, each
               positional parameter is properly quoted to expand to a single
               parameter again.

     #         (Read-only) Expands to the number of positional parameters, i.e.,
               the size of the positional parameter stack in decimal.

     0         (Read-only) Inside the scope of a defined and called macro this
               expands to the name of the calling macro, or to the empty string
               if the macro is running from top-level.  For the [Option]al
               regular expression search and replace operator of vexpr this
               expands to the entire matching expression.  It represents the
               program name in global context.

     1         (Read-only) Access of the positional parameter stack.  All
               further parameters can be accessed with this syntax, too, ‘2’,
               ‘3’ etc.; positional parameters can be shifted off the stack by
               calling shift.  The parameter stack contains, for example, the
               arguments of a called defined macro, the matching groups of the
               [Option]al regular expression search and replace expression of
               vexpr, and can be explicitly created or overwritten with the
               command vpospar.

     account   (Read-only) Is set to the active account.

     add-file-recipients
               (Boolean) When file or pipe recipients have been specified,
               mention them in the corresponding address fields of the message
               instead of silently stripping them from their recipient list.  By
               default such addressees are not mentioned.

     allnet    (Boolean) Causes only the local part to be evaluated when
               comparing addresses.

     append    (Boolean) Causes messages saved in the secondary mailbox MBOX to
               be appended to the end rather than prepended.  This should always
               be set.

     askatend  (Boolean) Causes the prompts for ‘Cc:’ and ‘Bcc:’ lists to appear
               after the message has been edited.

     askattach
               (Boolean) If set, Mail asks an interactive user for files to
               attach at the end of each message; An empty line finalizes the
               list.

     askcc     (Boolean) Causes the interactive user to be prompted for carbon
               copy recipients (at the end of each message if askatend or
               bsdcompat are set).

     askbcc    (Boolean) Causes the interactive user to be prompted for blind
               carbon copy recipients (at the end of each message if askatend or
               bsdcompat are set).

     asksend   (Boolean) Causes the interactive user to be prompted for
               confirmation to send the message or reenter compose mode after
               having been shown an envelope summary.  This is by default
               enabled.

     asksign   (Boolean)[Option] Causes the interactive user to be prompted if
               the message is to be signed at the end of each message.  The
               smime-sign variable is ignored when this variable is set.

     asksub    (Boolean) Causes Mail to prompt the interactive user for the
               subject upon entering compose mode unless a subject already
               exists.

     attrlist  A sequence of characters to display in the ‘attribute’ column of
               the headline as shown in the display of headers; each for one
               type of messages (see Message states), with the default being
               ‘NUROSPMFAT+-$~’ or ‘NU  *HMFAT+-$~’ if the bsdflags variable is
               set, in the following order:

               ‘N’       new.
               ‘U’       unread but old.
               ‘R’       new but read.
               ‘O’       read and old.
               ‘S’       saved.
               ‘P’       preserved.
               ‘M’       mboxed.
               ‘F’       flagged.
               ‘A’       answered.
               ‘T’       draft.
               ‘+’       [v15 behaviour may differ] start of a (collapsed)
                         thread in threaded mode (see autosort, thread);
               ‘-’       [v15 behaviour may differ] an uncollapsed thread in
                         threaded mode; only used in conjunction with -L.
               ‘$’       classified as spam.
               ‘~’       classified as possible spam.

     autobcc   Specifies a list of recipients to which a blind carbon copy of
               each outgoing message will be sent automatically.

     autocc    Specifies a list of recipients to which a carbon copy of each
               outgoing message will be sent automatically.

     autocollapse
               (Boolean) Causes threads to be collapsed automatically when .Ql
               thread Ns ed sort mode is entered (see the collapse command).

     autoprint
               (Boolean) Enable automatic typeing of a(n existing) “successive”
               message after delete and undelete commands: the message that
               becomes the new “dot” is shown automatically, as via dp or dt.

     autosort  Causes sorted mode (see the sort command) to be entered
               automatically with the value of this variable as sorting method
               when a folder is opened, for example ‘set autosort=thread’.

     bang      (Boolean) Enables the substitution of all not (reverse-solidus)
               escaped exclamation mark ‘!’ characters by the contents of the
               last executed command for the ! shell escape command and ~!, one
               of the compose mode COMMAND ESCAPES.  If this variable is not set
               no reverse solidus stripping is performed.

     bind-timeout
               [Obsolete] Predecessor of bind-inter-byte-timeout.  [v15
               behaviour may differ] Setting this automatically sets the
               successor.

     bind-inter-byte-timeout
               [Option] Terminals may generate multi-byte sequences for special
               function keys, for example, but these sequences may not become
               read as a unit.  And multi-byte sequences can be defined freely
               via bind.  This variable specifies the timeout in milliseconds
               that the MLE (see On terminal control and line editor) waits for
               more bytes to arrive unless it considers a sequence “complete”.
               The default is 200, the maximum is about 10 seconds.  In the
               following example the comments state which sequences are affected
               by this timeout:

                     ? bind base abc echo 0 # abc
                     ? bind base ab,c echo 1 # ab
                     ? bind base abc,d echo 2 # abc
                     ? bind base ac,d echo 3 # ac
                     ? bind base a,b,c echo 4
                     ? bind base a,b,c,d echo 5
                     ? bind base a,b,cc,dd echo 6 # cc and dd

     bind-inter-key-timeout
               [Option] Multi-key bind sequences do not time out by default.  If
               this variable is set, then the current key sequence is forcefully
               terminated once the timeout (in milliseconds) triggers.  The
               value should be (maybe significantly) larger than
               bind-inter-byte-timeout, but may not excess the maximum, too.

     bsdcompat
               (Boolean) Sets some cosmetical features to traditional BSD style;
               has the same affect as setting askatend and all other variables
               prefixed with ‘bsd’; it also changes the behaviour of emptystart
               (which does not exist in BSD).

     bsdflags  (Boolean) Changes the letters shown in the first column of a
               header summary to traditional BSD style.

     bsdheadline
               (Boolean) Changes the display of columns in a header summary to
               traditional BSD style.

     bsdmsgs   (Boolean) Changes some informational messages to traditional BSD
               style.

     bsdorder  (Boolean) Causes the ‘Subject:’ field to appear immediately after
               the ‘To:’ field in message headers and with the ~h COMMAND
               ESCAPES.

     build-cc, build-ld, build-os, build-rest
               (Read-only) The build environment, including the compiler, the
               linker, the operating system Mail has been build for, usually
               taken from uname(1) via ‘uname -s’, and then lowercased, as well
               as all the possibly interesting rest of the configuration and
               build environment.  This information is also available in the
               verbose output of the command version.

     charset-7bit
               The value that should appear in the ‘charset=’ parameter of
               ‘Content-Type:’ MIME header fields when no character set
               conversion of the message data was performed.  This defaults to
               US-ASCII, and the chosen character set should be US-ASCII
               compatible.

     charset-8bit
               [Option] The default 8-bit character set that is used as an
               implicit last member of the variable sendcharsets.  This defaults
               to UTF-8 if character set conversion capabilities are available,
               and to ISO-8859-1 otherwise (unless the operating system
               environment is known to always and exclusively support UTF-8
               locales), in which case the only supported character set is
               ttycharset and this variable is effectively ignored.

     charset-unknown-8bit
               [Option] RFC 1428 specifies conditions when internet mail
               gateways shall “upgrade” the content of a mail message by using a
               character set with the name ‘unknown-8bit’.  Because of the
               unclassified nature of this character set Mail will not be
               capable to convert this character set to any other character set.
               If this variable is set any message part which uses the character
               set ‘unknown-8bit’ is assumed to really be in the character set
               given in the value, otherwise the (final) value of charset-8bit
               is used for this purpose.

               This variable will also be taken into account if a MIME type (see
               The mime.types files) of a MIME message part that uses the
               ‘binary’ character set is forcefully treated as text.

     cmd       The default value for the pipe command.

     colour-disable
               (Boolean)[Option] Forcefully disable usage of colours.  Also see
               the section Coloured display.

     colour-pager
               (Boolean)[Option] Whether colour shall be used for output that is
               paged through PAGER.  Note that pagers may need special command
               line options, for example less(1) requires the option -R and
               lv(1) the option -c in order to support colours.  Often doing
               manual adjustments is unnecessary since Mail may perform
               adjustments dependent on the value of the environment variable
               PAGER (see there for more).

     contact-mail, contact-web
               (Read-only) Addresses for contact per email and web,
               respectively, for bug reports, suggestions, or anything else
               regarding Mail.  The former can be used directly: ‘? eval mail
               $contact-mail’.

     content-description-forwarded-message,
               content-description-quote-attachment,
               content-description-smime-message,
               content-description-smime-signature
               [Option](partially) Strings which will be placed in according
               ‘Content-Description:’ headers if non-empty.  They all have
               default values, for example ‘Forwarded message’.

     crt       In a(n interactive) terminal session, then if this valued
               variable is set it will be used as a threshold to determine how
               many lines the given output has to span before it will be
               displayed via the configured PAGER; Usage of the PAGER can be
               forced by setting this to the value ‘0’, setting it without a
               value will deduce the current height of the terminal screen to
               compute the threshold (see LINES, screen and stty(1)).  [v15
               behaviour may differ] At the moment this uses the count of lines
               of the message in wire format, which, dependent on the
               mime-encoding of the message, is unrelated to the number of
               display lines.  (The software is old and historically the
               relation was a given thing.)

     customhdr
               Define a set of custom headers to be injected into newly composed
               or forwarded messages.  A custom header consists of the field
               name followed by a colon ‘:’ and the field content body.
               Standard header field names cannot be overwritten by a custom
               header.  Different to the command line option -C the variable
               value is interpreted as a comma-separated list of custom headers:
               to include commas in header bodies they need to become escaped
               with reverse solidus ‘\’.  Headers can be managed more freely in
               compose mode via ~^.

                     ? set customhdr='Hdr1: Body1-1\, Body1-2, Hdr2: Body2'

     datefield
               Controls the appearance of the ‘%d’ date and time format
               specification of the headline variable, that is used, for
               example, when viewing the summary of headers.  If unset, then the
               local receiving date is used and displayed unformatted, otherwise
               the message sending ‘Date:’.  It is possible to assign a
               strftime(3) format string and control formatting, but embedding
               newlines via the ‘%n’ format is not supported, and will result in
               display errors.  The default is ‘%Y-%m-%d %H:%M’, and also see
               datefield-markout-older.

     datefield-markout-older
               Only used in conjunction with datefield.  Can be used to create a
               visible distinction of messages dated more than a day in the
               future, or older than six months, a concept comparable to the -l
               option of the POSIX utility ls(1).  If set to the empty string,
               then the plain month, day and year of the ‘Date:’ will be
               displayed, but a strftime(3) format string to control formatting
               can be assigned.  The default is ‘%Y-%m-%d’.

     debug     (Boolean) (Almost) Enter a debug-only sandbox mode which
               generates many log messages, disables the actual delivery of
               messages, and also implies norecord as well as nosave.  Also see
               verbose.

     disposition-notification-send
               (Boolean)[Option] Emit a ‘Disposition-Notification-To:’ header
               (RFC 3798) with the message.  This requires the from variable to
               be set.

     dot       (Boolean) When dot is set, a period ‘.’ on a line by itself
               during message input in (interactive or batch -#) compose mode
               will be treated as end-of-message (in addition to the normal end-
               of-file condition).  This behaviour is implied in posix mode with
               a set ignoreeof.

     dotlock-disable
               (Boolean)[Option] Disable creation of dotlock files for MBOX
               databases.

     dotlock-ignore-error
               [Obsolete](Boolean)[Option] Ignore failures when creating dotlock
               files.  Please use dotlock-disable instead.

     editalong
               If this variable is set then the editor is started automatically
               when a message is composed in interactive mode.  If the value
               starts with the letter ‘v’ then this acts as if ~v, otherwise as
               if ~e (see COMMAND ESCAPES) had been specified.  The editheaders
               variable is implied for this automatically spawned editor
               session.

     editheaders
               (Boolean) When a message is edited while being composed, its
               header is included in the editable text.

     emptystart
               (Boolean) When entering interactive mode Mail normally writes “No
               mail for user” and exits immediately if a mailbox is empty or
               does not exist.  If this variable is set Mail starts even with an
               empty or non-existent mailbox (the latter behaviour furtherly
               depends upon bsdcompat, though).

     errexit   (Boolean) Let each command with a non-0 exit status, including
               every called macro which returns a non-0 status, cause a program
               exit unless prefixed by ignerr (see Command modifiers).  This
               also affects COMMAND ESCAPES, but which use a different modifier
               for ignoring the error.  Please refer to the variable ? for more
               on this topic.

     escape    The first character of this value defines the escape character
               for COMMAND ESCAPES in compose mode.  The default value is the
               character tilde ‘~’.  If set to the empty string, command escapes
               are disabled.

     expandaddr
               If unset then file and command pipeline address targets are not
               allowed, and any such address will be filtered out, giving a
               warning message.  If set then all possible recipient address
               specifications will be accepted, unless the optional value is
               more specific (also see On sending mail, and non-interactive
               mode).  If the value contains ‘restrict’ then behaviour equals
               the former unless in interactive mode, or when tilde commands
               were enabled explicitly via -~ or -#, in which case it equals the
               latter, and thus allows all addressees.  ‘restrict’ really acts
               like ‘restrict,-all,+name,+addr’, so care for ordering issues
               must be taken.

               Indeed the value is interpreted as a comma-separated list of
               case-insensitive strings.  Hard send errors can be enforced for
               disallowed address types by setting ‘fail’; by default these are
               only filtered out.  User name receivers addressing valid local
               users can be expanded to a network address (also see hostname) by
               setting ‘nametoaddr’.  Address targets can be added and removed
               with a plus sign ‘+’ or hyphen-minus ‘-’ prefix, respectively:
               the value ‘all’ addresses all possible specifications, ‘fcc’
               whitelists targets specified via ‘Fcc:’ headers regardless of
               other settings, ‘file’ file targets (it includes ‘fcc’), ‘pipe’
               command pipeline targets, ‘name’ plain user names left for
               further expansion by the MTA (implicitly disallowed for the SMTP
               based mta), and ‘addr’ network addresses.  Targets are
               interpreted in the given order, so that ‘restrict,fail,+file,
               -all,+addr’ will cause hard errors for any non-network address
               recipient address unless running interactively or having been
               started with the option -~ or -#; in the latter case(s) any
               address may be used, then.

               Historically invalid network addressees were silently stripped
               off — shall they cause hard errors instead it must be ensured
               that ‘failinvaddr’ is an entry of the list (it really acts like
               ‘failinvaddr,+addr’).  Likewise, ‘domaincheck’ (actually
               ‘domaincheck,+addr’) compares address domain names against a
               whitelist and strips off (‘fail’ for hard errors) addressees
               which fail this test; the domain name ‘localhost’ and the non-
               empty value of hostname (the real hostname otherwise) are always
               whitelisted, expandaddr-domaincheck can be set to extend this
               list.  Finally some address providers (for example -b, -c and all
               other command line recipients) will be evaluated as if specified
               within dollar-single-quotes (see Shell-style argument quoting) if
               the value list contains the string ‘shquote’.

     expandaddr-domaincheck
               Can be set to a comma-separated list of domain names which should
               be whitelisted for the evaluation of the ‘domaincheck’ mode of
               expandaddr.  IDNA encoding is not automatically performed,
               addrcodec can be used to prepare the domain (of an address).

     expandargv
               Unless this variable is set additional mta (Mail-Transfer-Agent)
               arguments from the command line, as can be given after a --
               separator, results in a program termination with failure status.
               The same can be accomplished by using the special (case-
               insensitive) value ‘fail’.  A lesser strict variant is the
               otherwise identical ‘restrict’, which does accept such arguments
               in interactive mode, or if tilde commands were enabled explicitly
               by using one of the command line options -~ or -#.  The empty
               value will allow unconditional usage.

     features  (Read-only) String giving a list of optional features.  Features
               are preceded with a plus sign ‘+’ if they are available, with a
               hyphen-minus ‘-’ otherwise.  To ease substring matching the
               string starts and ends with a comma.  The output of the command
               version includes this information in a more pleasant output.

     flipr     (Boolean) This setting reverses the meanings of a set of reply
               commands, turning the lowercase variants, which by default
               address all recipients included in the header of a message
               (reply, respond, followup) into the uppercase variants, which by
               default address the sender only (Reply, Respond, Followup) and
               vice versa.

     folder    The default path under which mailboxes are to be saved: filenames
               that begin with the plus sign ‘+’ will have the plus sign
               replaced with the value of this variable if set, otherwise the
               plus sign will remain unchanged when doing Filename
               transformations; also see folder for more on this topic, and know
               about standard imposed implications of outfolder.  The value
               supports a subset of transformations itself, and if the non-empty
               value does not start with a solidus ‘/’, then the value of HOME
               will be prefixed automatically.  Once the actual value is
               evaluated first, the internal variable folder-resolved will be
               updated for caching purposes.

     folder-hook-FOLDER, folder-hook
               Names a defined macro which will be called whenever a folder is
               opened.  The macro will also be invoked when new mail arrives,
               but message lists for commands executed from the macro only
               include newly arrived messages then.  localopts are activated by
               default in a folder hook, causing the covered settings to be
               reverted once the folder is left again.

               The specialized form will override the generic one if ‘FOLDER’
               matches the file that is opened.  Unlike other folder
               specifications, the fully expanded name of a folder, without
               metacharacters, is used to avoid ambiguities.  However, if the
               mailbox resides under folder then the usual ‘+’ specification is
               tried in addition, so that if folder is “mail” (and thus relative
               to the user's home directory) then /home/usr1/mail/sent will be
               tried as ‘folder-hook-/home/usr1/mail/sent’ first, but then
               followed by ‘folder-hook-+sent’.

     folder-resolved
               (Read-only) Set to the fully resolved path of folder once that
               evaluation has occurred; rather internal.

     followup-to
               (Boolean) Controls whether a ‘Mail-Followup-To:’ header is
               generated when sending messages to known mailing lists.  The user
               as determined via from (or, if that contains multiple addresses,
               sender) will be placed in there if any list addressee is not a
               subscribed list.  Also see followup-to-honour and the commands
               mlist, mlsubscribe, reply and Lreply.

     followup-to-add-cc
               (Boolean) Controls whether the user will be added to the
               messages' ‘Cc:’ list in addition to placing an entry in
               ‘Mail-Followup-To:’ (see followup-to).

     followup-to-honour
               Controls whether a ‘Mail-Followup-To:’ header is honoured when
               group-replying to a message via reply or Lreply.  This is a
               quadoption; if set without a value it defaults to “yes”, and see
               followup-to.

     forward-add-cc
               (Boolean) Whether the sender of a message quoted via ~Q shall be
               added to the messages' ‘Cc:’ list.

     forward-as-attachment
               (Boolean) Original messages are normally sent as inline text with
               the forward command, and only the first part of a multipart
               message is included.  With this setting enabled messages are sent
               as unmodified MIME ‘message/rfc822’ attachments with all of their
               parts included.

     forward-inject-head, forward-inject-tail
               The strings to put before and after the text of a message with
               the forward command, respectively.  The former defaults to
               ‘-------- Original Message --------\n’.  Special format
               directives in these strings will be expanded if possible, and if
               so configured the output will be folded according to quote-fold;
               for more please refer to quote-inject-head.  Injections will not
               be performed by forward if the variable forward-as-attachment is
               set — the COMMAND ESCAPES ~F, ~f, ~M, ~m, ~U, ~u always inject.

     from      The address (or a list of addresses) to put into the ‘From:’
               field of the message header, quoting RFC 5322: the author(s) of
               the message, that is, the mailbox(es) of the person(s) or
               system(s) responsible for the writing of the message.  According
               to that RFC setting the sender variable is required if from
               contains more than one address.  [v15 behaviour may differ]
               Please expect automatic management of the from and sender
               relationship.  Dependent on the context these addresses are
               handled as if they were in the list of alternates.

               If a file-based MTA is used, then from (or, if that contains
               multiple addresses, sender) can nonetheless be used as the
               envelope sender address at the MTA protocol level (the RFC 5321
               reverse-path), either via the -r command line option (without
               argument; see there for more), or by setting r-option-implicit.

               If the machine's hostname is not valid at the Internet (for
               example at a dialup machine), then either this variable or
               hostname ([v15-compat] a SMTP-based mta adds even more fine-
               tuning capabilities with smtp-hostname) have to be set: if so the
               message and MIME part related unique ID fields ‘Message-ID:’ and
               ‘Content-ID:’ will be created (except when disallowed by
               message-id-disable or stealthmua).

     fullnames
               (Boolean) Due to historical reasons comments and name parts of
               email addresses are removed by default when sending mail,
               replying to or forwarding a message.  If this variable is set
               such stripping is not performed.

     fwdheading
               [Obsolete] Predecessor of forward-inject-head.

     header    (Boolean) Causes the header summary to be written at startup and
               after commands that affect the number of messages or the order of
               messages in the current folder.  Unless in posix mode a header
               summary will also be displayed on folder changes.  The command
               line option -N can be used to set noheader.

     headline  A format string to use for the summary of headers.  Format
               specifiers in the given string start with a percent sign ‘%’ and
               may be followed by an optional decimal number indicating the
               field width — if that is negative, the field is to be left-
               aligned.  Names and addresses are subject to modifications
               according to showname and showto.  Valid format specifiers are:

               ‘%%’      A plain percent sign.
               ‘%>’      “Dotmark”: a space character but for the current
                         message (“dot”), for which it expands to ‘>’ (dependent
                         on headline-plain).
               ‘%<’      “Dotmark”: a space character but for the current
                         message (“dot”), for which it expands to ‘<’ (dependent
                         on headline-plain).
               ‘%$’      [Option] The spam score of the message, as has been
                         classified via the command spamrate.  Shows only a
                         replacement character if there is no spam support.
               ‘%a’      Message attribute character (status flag); the actual
                         content can be adjusted by setting attrlist.
               ‘%d’      The date found in the ‘Date:’ header of the message
                         when datefield is set (the default), otherwise the date
                         when the message was received.  Formatting can be
                         controlled by assigning a strftime(3) format string to
                         datefield (and datefield-markout-older).
               ‘%e’      The indenting level in ‘thread’ed sort mode.
               ‘%f’      The address of the message sender.
               ‘%i’      The message thread tree structure.  (Note that this
                         format does not support a field width, and honours
                         headline-plain.)
               ‘%L’      Mailing list status: is the addressee of the message a
                         known ‘l’ (mlist) or ‘L’ mlsubscribed mailing list?
                         The letter ‘P’ announces the presence of a RFC 2369
                         ‘List-Post:’ header, which makes a message a valuable
                         target of Lreply.
               ‘%l’      The number of lines of the message, if available.
               ‘%m’      Message number.
               ‘%o’      The number of octets (bytes) in the message, if
                         available.
               ‘%S’      Message subject (if any) in double quotes.
               ‘%s’      Message subject (if any).
               ‘%t’      The position in threaded/sorted order.
               ‘%U’      The value 0 except in an IMAP mailbox, where it expands
                         to the UID of the message.

               The default is ‘%>%a%m %-18f %16d %4l/%-5o %i%-s’, or
               ‘%>%a%m %20-f  %16d %3l/%-5o %i%-S’ if bsdcompat is set.  Also
               see attrlist, headline-plain and headline-bidi.

     headline-bidi
               Bidirectional text requires special treatment when displaying
               headers, because numbers (in dates or for file sizes etc.) will
               not affect the current text direction, in effect resulting in
               ugly line layouts when arabic or other right-to-left text is to
               be displayed.  On the other hand only a minority of terminals is
               capable to correctly handle direction changes, so that user
               interaction is necessary for acceptable results.  Note that
               extended host system support is required nonetheless, e.g.,
               detection of the terminal character set is one precondition; and
               this feature only works in an Unicode (i.e., UTF-8) locale.

               In general setting this variable will cause Mail to encapsulate
               text fields that may occur when displaying headline (and some
               other fields, like dynamic expansions in prompt) with special
               Unicode control sequences; it is possible to fine-tune the
               terminal support level by assigning a value: no value (or any
               value other than ‘1’, ‘2’ and ‘3’) will make Mail assume that the
               terminal is capable to properly deal with Unicode version 6.3, in
               which case text is embedded in a pair of U+2068 (FIRST STRONG
               ISOLATE) and U+2069 (POP DIRECTIONAL ISOLATE) characters.  In
               addition no space on the line is reserved for these characters.

               Weaker support is chosen by using the value ‘1’ (Unicode 6.3, but
               reserve the room of two spaces for writing the control sequences
               onto the line).  The values ‘2’ and ‘3’ select Unicode 1.1
               support (U+200E, LEFT-TO-RIGHT MARK); the latter again reserves
               room for two spaces in addition.

     headline-plain
               (Boolean) On Unicode (UTF-8) aware terminals enhanced graphical
               symbols are used by default for certain entries of headline.  If
               this variable is set only basic US-ASCII symbols will be used.

     history-file
               [Option] The (expandable) location of a permanent history file
               for the MLE line editor (On terminal control and line editor).
               Also see history-size.

     history-gabby
               [Option] Add more entries to the MLE history as is normally done.
               A comma-separated list of case-insensitive strings can be used to
               fine-tune which gabby entries shall be allowed.  If it contains
               ‘errors’, erroneous commands will also be added.  ‘all’ adds all
               optional entries, and is the fallback chattiness identifier of
               on-history-addition.

     history-gabby-persist
               (Boolean)[Option] The history-gabby entries will not be saved in
               persistent storage unless this variable is set.  The knowledge of
               whether a persistent entry was gabby is not lost.  Also see
               history-file.

     history-size
               [Option] Setting this variable imposes a limit on the number of
               concurrent history entries.  If set to the value 0 then no
               further history entries will be added, and loading and
               incorporation of the history-file upon program startup can also
               be suppressed by doing this.  Runtime changes will not be
               reflected before the history is saved or loaded (again).

     hold      (Boolean) This setting controls whether messages are held in the
               system inbox, and it is set by default.

     hostname  Used instead of the value obtained from uname(3) and
               getaddrinfo(3) as the hostname when expanding local addresses,
               for example in ‘From:’ (also see On sending mail, and non-
               interactive mode, for expansion of addresses that have a valid
               user-, but no domain name in angle brackets).  If either of from
               or this variable is set the message and MIME part related unique
               ID fields ‘Message-ID:’ and ‘Content-ID:’ will be created (except
               when disallowed by message-id-disable or stealthmua).  If the
               [Option]al IDNA support is available (see idna-disable) variable
               assignment is aborted when a necessary conversion fails.

               Setting it to the empty string will cause the normal hostname to
               be used, but nonetheless enables creation of said ID fields.
               [v15-compat] in conjunction with the built-in SMTP mta
               smtp-hostname also influences the results: one should produce
               some test messages with the desired combination of hostname,
               and/or from, sender etc. first.

     idna-disable
               (Boolean)[Option] Can be used to turn off the automatic
               conversion of domain names according to the rules of IDNA
               (internationalized domain names for applications).  Since the
               IDNA code assumes that domain names are specified with the
               ttycharset character set, an UTF-8 locale charset is required to
               represent all possible international domain names (before
               conversion, that is).

     ifs       The input field separator that is used ([v15 behaviour may
               differ] by some functions) to determine where to split input
               data.

               1.        Unsetting is treated as assigning the default value, ‘
                         \t\n’.
               2.        If set to the empty value, no field splitting will be
                         performed.
               3.        If set to a non-empty value, all whitespace characters
                         are extracted and assigned to the variable ifs-ws.

               a.        ifs-ws will be ignored at the beginning and end of
                         input.  Diverging from POSIX shells default whitespace
                         is removed in addition, which is owed to the entirely
                         different line content extraction rules.
               b.        Each occurrence of a character of ifs will cause field-
                         splitting, any adjacent ifs-ws characters will be
                         skipped.

     ifs-ws    (Read-only) Automatically deduced from the whitespace characters
               in ifs.

     ignore    (Boolean) Ignore interrupt signals from the terminal while
               entering messages; instead echo them as ‘@’ characters and
               discard the current line.

     ignoreeof
               (Boolean) Ignore end-of-file conditions (‘control-D’) in compose
               mode on message input and in interactive command input.  If set
               an interactive command input session can only be left by
               explicitly using one of the commands exit and quit, and message
               input in compose mode can only be terminated by entering a period
               ‘.’ on a line by itself or by using the ~. COMMAND ESCAPES;
               Setting this implies the behaviour that dot describes in posix
               mode.

     inbox     If this is set to a non-empty string it will specify the user's
               primary system mailbox, overriding MAIL and the system-dependent
               default, and (thus) be used to replace ‘%’ when doing Filename
               transformations; also see folder for more on this topic.  The
               value supports a subset of transformations itself.

     indentprefix
               String used by the ~m, ~M and ~R COMMAND ESCAPES and by the quote
               option for indenting messages, in place of the POSIX mandated
               default tabulator character ‘\t’.  Also see quote-chars.

     keep      (Boolean) If set, an empty primary system mailbox file is not
               removed.  Note that, in conjunction with posix mode any empty
               file will be removed unless this variable is set.  This may
               improve the interoperability with other mail user agents when
               using a common folder directory, and prevents malicious users
               from creating fake mailboxes in a world-writable spool directory.
               [v15 behaviour may differ] Only local regular (MBOX) files are
               covered, Maildir and other mailbox types will never be removed,
               even if empty.

     keep-content-length
               (Boolean) When (editing messages and) writing MBOX mailbox files
               Mail can be told to keep the ‘Content-Length:’ and ‘Lines:’
               header fields that some MUAs generate by setting this variable.
               Since Mail does neither use nor update these non-standardized
               header fields (which in itself shows one of their conceptual
               problems), stripping them should increase interoperability in
               between MUAs that work with with same mailbox files.  Note that,
               if this is not set but writebackedited, as below, is, a possibly
               performed automatic stripping of these header fields already
               marks the message as being modified.  [v15 behaviour may differ]
               At some future time Mail will be capable to rewrite and apply an
               mime-encoding to modified messages, and then those fields will be
               stripped silently.

     keepsave  (Boolean) When a message is saved it is usually discarded from
               the originating folder when Mail is quit.  This setting causes
               all saved message to be retained.

     line-editor-cpl-word-breaks
               [Option] List of bytes which are used by the mle-complete
               tabulator completion to decide where word boundaries exist, by
               default ‘"'@=;|:’ [v15 behaviour may differ] This mechanism is
               yet restricted.

     line-editor-disable
               (Boolean) Turn off any line editing capabilities (from Mails POW,
               see On terminal control and line editor for more).

     line-editor-no-defaults
               (Boolean)[Option] Do not establish any default key binding.

     log-prefix
               Error log message prefix string (‘mail: ’).

     mailbox-display
               (Read-only) The name of the current mailbox (folder), possibly
               abbreviated for display purposes.

     mailbox-resolved
               (Read-only) The fully resolved path of the current mailbox.

     mailcap-disable
               (Boolean)[Option] Turn off consideration of MIME type handlers
               from, and implicit loading of The Mailcap files.

     mailx-extra-rc
               An additional startup file that is loaded as the last of the
               Resource files.  Use this file for commands that are not
               understood by other POSIX mailx(1) implementations, i.e., mostly
               anything which is not covered by Initial settings.

     markanswered
               (Boolean) When a message is replied to and this variable is set,
               it is marked as having been answered.  See the section Message
               states.

     mbox-fcc-and-pcc
               (Boolean) By default all file and pipe message receivers (see
               expandaddr) will be fed valid MBOX database entry message data
               (see folder, mbox-rfc4155), and existing file targets will become
               extended in compliance to RFC 4155.  If this variable is unset
               then a plain standalone RFC 5322 message will be written, and
               existing file targets will be overwritten.

     mbox-rfc4155
               (Boolean) When opening MBOX mailbox databases, and in order to
               achieve compatibility with old software, the very tolerant POSIX
               standard rules for detecting message boundaries (so-called
               ‘From_’ lines) are used instead of the stricter rules from the
               standard RFC 4155.  This behaviour can be switched by setting
               this variable.

               This may temporarily be handy when Mail complains about invalid
               ‘From_’ lines when opening a MBOX: in this case setting this
               variable and re-opening the mailbox in question may correct the
               result.  If so, copying the entire mailbox to some other file, as
               in ‘copy * SOME-FILE’, will perform proper, all-compatible
               ‘From_’ quoting for all detected messages, resulting in a valid
               MBOX mailbox.  ([v15 behaviour may differ] The better and non-
               destructive approach is to re-encode invalid messages, as if it
               would be created anew, instead of mangling the ‘From_’ lines;
               this requires the structural code changes of the v15 rewrite.)
               Finally the variable can be unset again:

                     define mboxfix {
                       localopts yes; wysh set mbox-rfc4155;\
                         wysh File "${1}"; copy * "${2}"
                     }
                     call mboxfix /tmp/bad.mbox /tmp/good.mbox

     memdebug  (Boolean) Internal development variable.  (Keeps memory debug
               enabled even if debug is not set.)

     message-id-disable
               (Boolean) By setting this variable the generation of
               ‘Message-ID:’ and ‘Content-ID:’ message and MIME part headers can
               be completely suppressed, effectively leaving this task up to the
               mta (Mail-Transfer-Agent) or the SMTP server.  Note that
               according to RFC 5321 a SMTP server is not required to add this
               field by itself, so it should be ensured that it accepts messages
               without ‘Message-ID’.

     message-inject-head
               A string to put at the beginning of each new message, followed by
               a newline.  [Obsolete] The escape sequences tabulator ‘\t’ and
               newline ‘\n’ are understood (use the wysh prefix when setting the
               variable(s) instead).

     message-inject-tail
               A string to put at the end of each new message, followed by a
               newline.  [Obsolete] The escape sequences tabulator ‘\t’ and
               newline ‘\n’ are understood (use the wysh prefix when setting the
               variable(s) instead).  Also see on-compose-leave.

     metoo     (Boolean) Usually, when an alias expansion contains the sender,
               the sender is removed from the expansion.  Setting this option
               suppresses these removals.  Note that a set metoo also causes a
               ‘-m’ option to be passed through to the mta (Mail-Transfer-
               Agent); though most of the modern MTAs no longer document this
               flag, no MTA is known which does not support it (for historical
               compatibility).

     mime-allow-text-controls
               (Boolean) When sending messages, each part of the message is
               MIME-inspected in order to classify the ‘Content-Type:’ and
               ‘Content-Transfer-Encoding:’ (see mime-encoding) that is required
               to send this part over mail transport, i.e., a computation rather
               similar to what the file(1) command produces when used with the
               ‘--mime’ option.

               This classification however treats text files which are encoded
               in UTF-16 (seen for HTML files) and similar character sets as
               binary octet-streams, forcefully changing any ‘text/plain’ or
               ‘text/html’ specification to ‘application/octet-stream’: If that
               actually happens a yet unset charset MIME parameter is set to
               ‘binary’, effectively making it impossible for the receiving MUA
               to automatically interpret the contents of the part.

               If this variable is set, and the data was unambiguously
               identified as text data at first glance (by a ‘.txt’ or ‘.html’
               file extension), then the original ‘Content-Type:’ will not be
               overwritten.

     mime-alternative-favour-rich
               (Boolean) If this variable is set then rich MIME alternative
               parts (e.g., HTML) will be preferred in favour of included plain
               text versions when displaying messages, provided that a handler
               exists which produces output that can be (re)integrated into
               Mail's normal visual display.

     mime-counter-evidence
               Normally the ‘Content-Type:’ field is used to decide how to
               handle MIME parts.  Some MUAs, however, do not use The mime.types
               files (also see HTML mail and MIME attachments) or a similar
               mechanism to correctly classify content, but specify an
               unspecific MIME type (‘application/octet-stream’) even for plain
               text attachments.  If this variable is set then Mail will try to
               re-classify such MIME message parts, if possible, for example via
               a possibly existing attachment filename.  A non-empty value may
               also be given, in which case a number is expected, actually a
               carrier of bits, best specified as a binary value, like ‘0b1111’.

               If bit two is set (counting from 1, decimal 2) then the
                   detected mimetype will be carried along with the message and
                   be used for deciding which MIME handler is to be used, for
                   example; when displaying such a MIME part the part-info will
                   indicate the overridden content-type by showing a plus sign
                   ‘+’.
               If bit three is set (decimal 4) then the counter-evidence is
                   always produced and a positive result will be used as the
                   MIME type, even forcefully overriding the parts given MIME
                   type.
               If bit four is set (decimal 8) as a last resort the actual
                   content of ‘application/octet-stream’ parts will be
                   inspected, so that data which looks like plain text can be
                   treated as such.  This mode is even more relaxed when data is
                   to be displayed to the user or used as a message quote (data
                   consumers which mangle data for display purposes, which
                   includes masking of control characters, for example).

     mime-encoding
               The MIME ‘Content-Transfer-Encoding’ to use in outgoing text
               messages and message parts, where applicable (7-bit clean text
               messages are without an encoding if possible):

               ‘8bit’    (Or ‘8b’.)  8-bit transport effectively causes the raw
                         data be passed through unchanged, but may cause
                         problems when transferring mail messages over channels
                         that are not ESMTP (RFC 1869) compliant.  Also, several
                         input data constructs are not allowed by the
                         specifications and may cause a different transfer-
                         encoding to be used.  By established rules and popular
                         demand occurrences of ‘^From_’ (see mbox-rfc4155) will
                         be MBOXO quoted (prefixed with greater-than sign ‘>’)
                         instead of causing a non-destructive encoding like
                         ‘quoted-printable’ to be chosen, unless context (like
                         message signing) requires otherwise.
               ‘quoted-printable’
                         (Or ‘qp’.)  Quoted-printable encoding is 7-bit clean
                         and has the property that ASCII characters are passed
                         through unchanged, so that an english message can be
                         read as-is; it is also acceptable for other single-byte
                         locales that share many characters with ASCII, for
                         example ISO-8859-1.  The encoding will cause a large
                         overhead for messages in other character sets: for
                         example it will require up to twelve (12) bytes to
                         encode a single UTF-8 character of four (4) bytes.  It
                         is the default encoding.
               ‘base64’  (Or ‘b64’.)  This encoding is 7-bit clean and will
                         always be used for binary data.  This encoding has a
                         constant input:output ratio of 3:4, regardless of the
                         character set of the input data it will encode three
                         bytes of input to four bytes of output.  This transfer-
                         encoding is not human readable without performing a
                         decoding step.

     mime-force-sendout
               (Boolean)[Option] Whenever it is not acceptable to fail sending
               out messages because of non-convertible character content this
               variable may be set.  It will, as a last resort, classify the
               part content as ‘application/octet-stream’.  Please refer to the
               section Character sets for the complete picture of character set
               conversion in Mail.

     mimetypes-load-control
               Can be used to control which of The mime.types files are loaded:
               if the letter ‘u’ is part of the option value, then the user's
               personal ~/.mime.types file will be loaded (if it exists);
               likewise the letter ‘s’ controls loading of the system wide /etc/
               mime.types; directives found in the user file take precedence,
               letter matching is case-insensitive.  If this variable is not set
               Mail will try to load both files.  Incorporation of the
               Mail-built-in MIME types cannot be suppressed, but they will be
               matched last (the order can be listed via mimetype).

               More sources can be specified by using a different syntax: if the
               value string contains an equals sign ‘=’ then it is instead
               parsed as a comma-separated list of the described letters plus
               ‘f=FILENAME’ pairs; the given filenames will be expanded and
               loaded, and their content may use the extended syntax that is
               described in the section The mime.types files.  Directives found
               in such files always take precedence (are prepended to the MIME
               type cache).

     mta       Select an alternate Mail-Transfer-Agent by either specifying the
               full pathname of an executable (a ‘file://’ prefix may be given),
               or [Option]ally a SMTP aka SUBMISSION protocol URL [v15-compat]:

                     submissions://[user[:password]@]server[:port]

               ([no v15-compat]: ‘[smtp://]server[:port]’.)  The default has
               been chosen at compile time.  MTA data transfers are always
               performed in asynchronous child processes, and without
               supervision unless either the sendwait or the verbose variable is
               set.  ‘Bcc:’ headers are not passed through to MTAs as part of
               messages unless mta-bcc-ok is set (see there); corresponding
               receivers are addressed by protocol-specific means or MTA command
               line options only until then.  [Option]ally expansion of the
               well-known mta-aliases (aliases(5)) can also be directly
               performed by Mail.

               For testing purposes there is the ‘test’ pseudo-MTA, which dumps
               to standard output or optionally to a file, and honours
               mbox-fcc-and-pcc:

                     $ echo text | mail -:/ -Smta=test -s ubject ex@am.ple
                     $ </dev/null mail -:/ -Smta=test://./xy ex@am.ple

               For a file-based MTA it may be necessary to set mta-argv0 in in
               order to choose the right target of a modern mailwrapper(8)
               environment.  It will be passed command line arguments from
               several possible sources: from the variable mta-arguments if set,
               from the command line if given and the variable expandargv allows
               their use.  Argument processing of the MTA will be terminated
               with a -- separator.

               The otherwise occurring implicit usage of the following MTA
               command line arguments can be disabled by setting the boolean
               variable mta-no-default-arguments (which will also disable
               passing -- to the MTA): -i (for not treating a line with only a
               dot ‘.’ character as the end of input), -m (shall the variable
               metoo be set) and -v (if the verbose variable is set); in
               conjunction with the -r command line option Mail will also (not)
               pass -f as well as possibly -F.

               [Option]ally Mail can send mail over SMTP aka SUBMISSION network
               connections to a single defined smart host by setting this
               variable to a SMTP or SUBMISSION URL (see On URL syntax and
               credential lookup).  An authentication scheme can be specified
               via the variable chain smtp-auth.  Encrypted network connections
               are [Option]ally available, the section Encrypted network
               communication should give an overview and provide links to more
               information on this.  Note that with some mail providers it may
               be necessary to set the smtp-hostname variable in order to use a
               specific combination of from, hostname and mta.  Network
               communication socket timeouts are configurable via
               socket-connect-timeout.  All generated network traffic may be
               proxied over a SOCKS socks-proxy, it can be logged by setting
               verbose twice.  The following SMTP variants may be used:

               The plain SMTP protocol (RFC 5321) that normally lives on the
                   server port 25 and requires setting the smtp-use-starttls
                   variable to enter a TLS encrypted session state.  Assign a
                   value like [v15-compat]
                   ‘smtp://[user[:password]@]server[:port]’ ([no v15-compat]
                   ‘smtp://server[:port]’) to choose this protocol.

               The so-called SMTPS which is supposed to live on server port
                   465 and is automatically TLS secured.  Unfortunately it never
                   became a standardized protocol and may thus not be supported
                   by your hosts network service database – in fact the port
                   number has already been reassigned to other protocols!

                   SMTPS is nonetheless a commonly offered protocol and thus can
                   be chosen by assigning a value like [v15-compat]
                   ‘smtps://[user[:password]@]server[:port]’ ([no v15-compat]
                   ‘smtps://server[:port]’); due to the mentioned problems it is
                   usually necessary to explicitly specify the port as ‘:465’,
                   however.

               The SUBMISSION protocol (RFC 6409) lives on server port 587
                   and is identically to the SMTP protocol from Mail's point of
                   view; it requires setting smtp-use-starttls to enter a TLS
                   secured session state; e.g., [v15-compat]
                   ‘submission://[user[:password]@]server[:port]’.

               The SUBMISSIONS protocol (RFC 8314) that lives on server port
                   465 and is TLS secured by default.  It can be chosen by
                   assigning a value like [v15-compat]
                   ‘submissions://[user[:password]@]server[:port]’.  Due to the
                   problems mentioned for SMTPS above and the fact that
                   SUBMISSIONS is new and a successor that lives on the same
                   port as the historical engineering mismanagement named SMTPS,
                   it is usually necessary to explicitly specify the port as
                   ‘:465’.

     mta-aliases
               [Option] If set to a path pointing to a text file in valid MTA
               (Postfix) aliases(5) format, the file is loaded and cached
               (manageable with mtaaliases), and henceforth plain ‘name’ (see
               expandaddr) message receiver names are recursively expanded as a
               last expansion step, after the distribution lists which can be
               created with alias.  Constraints on aliases(5) content support:
               only local addresses (names) which are valid usernames
               (‘[a-z_][a-z0-9_-]*[$]?’) are treated as expandable aliases, and
               [v15 behaviour may differ] ‘:include:/file/name’ directives are
               not supported.  By including ‘-name’ in expandaddr it can be
               asserted that only expanded names (mail addresses) are passed
               through to the MTA.

     mta-arguments
               Arguments to pass through to a file-based mta can be given via
               this variable, which is parsed according to Shell-style argument
               quoting into an array of arguments, and which will be joined onto
               MTA options from other sources, and then passed individually to
               the MTA: ‘? wysh set mta-arguments='-t -X "/tmp/my log"'’.

     mta-no-default-arguments
               (Boolean) Unless this variable is set Mail will pass some well
               known standard command line options to a file-based mta (Mail-
               Transfer-Agent), see there for more.

     mta-no-receiver-arguments
               (Boolean) By default a file-based mta will be passed all receiver
               addresses on the command line.  Some MTAs impose special
               behaviour on such arguments, so setting this variable will
               suppress them altogether.  This can make it necessary to pass a
               -t via mta-arguments.

     mta-argv0
               Many systems use a so-called mailwrapper(8) environment to ensure
               compatibility with sendmail(1).  This works by inspecting the
               name that was used to invoke the mail delivery system.  If this
               variable is set then the mailwrapper (the program that is
               actually executed when calling the file-based mta) will treat its
               contents as that name.

     mta-bcc-ok
               (Boolean) By default ‘Bcc:’ header lines are not passed through
               since some MTAs do not remove them before sending them over the
               wire, in violation of RFC 5322.  (For example Exim and Courier
               would need to be started with the -t command line option to force
               stripping.)  Setting this enables pass-through, therefore avoids
               generation of mutilated message versions, and [v15 behaviour may
               differ] improves performance.

     netrc-lookup-USER@HOST, netrc-lookup-HOST, netrc-lookup
               (Boolean)[v15-compat][Option] Used to control usage of the user's
               ~/.netrc file for lookup of account credentials, as documented in
               the section On URL syntax and credential lookup and for the
               command netrc; the section The .netrc file documents the file
               format.  Also see netrc-pipe.

     netrc-pipe
               [v15-compat][Option] When ~/.netrc is loaded (see netrc and
               netrc-lookup) then Mail will read the output of a shell pipe
               instead of the user's ~/.netrc file if this variable is set (to
               the desired shell command).  This can be used to, for example,
               store ~/.netrc in encrypted form: ‘? set netrc-pipe='gpg -qd
               ~/.netrc.pgp'’.

     newfolders
               [Option] If this variable has the value ‘maildir’, newly created
               local folders will be in Maildir instead of MBOX format.

     newmail   Checks for new mail in the current folder each time the prompt is
               shown.  A Maildir folder must be re-scanned to determine if new
               mail has arrived.  If this variable is set to the special value
               ‘nopoll’ then a Maildir folder will not be rescanned completely,
               but only timestamp changes are detected.  Maildir folders are
               [Option]al.

     outfolder
               (Boolean) Causes a non-absolute filename specified in record, as
               well as the sender-based filenames of the Copy, Save, Followup
               and followup commands to be interpreted relative to the folder
               directory rather than relative to the current directory.

     on-account-cleanup-ACCOUNT, on-account-cleanup
               Macro hook which will be called once an account is left, as the
               very last step before unrolling per-account localopts.  This hook
               is run even in case of fatal errors, including those generated by
               switching to the account as such, and it is advisable to perform
               only absolutely necessary actions, like cleaning up alternates,
               for example.  The specialized form is used in favour of the
               generic one if found.

     on-compose-cleanup
               Macro hook which will be called after the message has been sent
               (or not, in case of failures), as the very last step before
               unrolling compose mode localopts.  This hook is run even in case
               of fatal errors, and it is advisable to perform only absolutely
               necessary actions, like cleaning up alternates, for example.

               For compose mode hooks that may affect the message content please
               see on-compose-enter, on-compose-leave, on-compose-splice.  [v15
               behaviour may differ] This hook exists because alias, alternates,
               commandalias, shortcut, to name a few, are neither covered by
               localopts nor by local: changes applied in compose mode will
               continue to be in effect thereafter.

     on-compose-enter, on-compose-leave
               Macro hooks which will be called once compose mode is entered,
               and after composing has been finished, respectively; the exact
               order of the steps taken is documented for ~., one of the COMMAND
               ESCAPES.  Context about the message being worked on can be
               queried via digmsg.  localopts are enabled for these hooks, and
               changes on variables will be forgotten after the message has been
               sent.  on-compose-cleanup can be used to perform other necessary
               cleanup steps.

               Here is an example that injects a signature via
               message-inject-tail; instead using on-compose-splice to simply
               inject the file of desire via ~< or ~<! may be a better approach.

                     define t_ocl {
                       vput ! i cat ~/.mysig
                       if $? -eq 0
                          vput csop message-inject-tail trim-end $i
                       end

                       # Alternatively
                       readctl create ~/.mysig
                       if $? -eq 0
                         readall i
                         if $? -eq 0
                           vput csop message-inject-tail trim-end $i
                         end
                         readctl remove ~/.mysig
                       end
                     }
                     set on-compose-leave=t_ocl

     on-compose-splice, on-compose-splice-shell
               These hooks run once the normal compose mode is finished, but
               before the on-compose-leave macro hook is called etc.  Both hooks
               will be executed in a subprocess, with their input and output
               connected to Mail such that they can act as if they would be an
               interactive user.  The difference in between them is that the
               latter is a SHELL command, whereas the former is a normal defined
               macro, but which is restricted to a small set of commands (the
               verbose output of for example list will indicate said
               capability).  localopts are enabled for these hooks (in the
               parent process), causing any setting to be forgotten after the
               message has been sent; on-compose-cleanup can be used to perform
               other cleanup as necessary.

               During execution of these hooks Mail will temporarily forget
               whether it has been started in interactive mode, (a restricted
               set of) COMMAND ESCAPES will always be available, and for
               guaranteed reproducibilities sake escape and ifs will be set to
               their defaults.  The compose mode command ~^ has been especially
               designed for scriptability (via these hooks).  The first line the
               hook will read on its standard input is the protocol version of
               said command escape, currently “0 0 2”: backward incompatible
               protocol changes have to be expected.

               Care must be taken to avoid deadlocks and other false control
               flow: if both involved processes wait for more input to happen at
               the same time, or one does not expect more input but the other is
               stuck waiting for consumption of its output, etc.  There is no
               automatic synchronization of the hook: it will not be stopped
               automatically just because it, e.g., emits ‘~x’.  The hooks will
               however receive a termination signal if the parent enters an
               error condition.  [v15 behaviour may differ] Protection against
               and interaction with signals is not yet given; it is likely that
               in the future these scripts will be placed in an isolated
               session, which is signalled in its entirety as necessary.

                     define ocs_signature {
                       read version
                       echo '~< ~/.mysig' # '~<! fortune pathtofortunefile'
                     }
                     set on-compose-splice=ocs_signature

                     wysh set on-compose-splice-shell=$'\
                       read version;\
                       printf "hello $version!  Headers: ";\
                       echo \'~^header list\';\
                       read status result;\
                       echo "status=$status result=$result";\
                       '

                     define ocsm {
                       read version
                       echo Splice protocol version is $version
                       echo '~^h l'; read hl; vput csop es subs "${hl}" 0 1
                       if "$es" != 2
                         echoerr 'Cannot read header list'; echo '~x'; xit
                       endif
                       if "$hl" !%?case ' cc'
                         echo '~^h i cc "Diet is your <mirr.or>"'; read es;\
                           vput csop es substring "${es}" 0 1
                         if "$es" != 2
                           echoerr 'Cannot insert Cc: header'; echo '~x'
                           # (no xit, macro finishes anyway)
                         endif
                       endif
                     }
                     set on-compose-splice=ocsm

     on-history-addition
               This hook will be called if an entry is about to be added to the
               history of the MLE, as documented in On terminal control and line
               editor.  It will be called with three arguments: the first is the
               name of the input context (see bind), the second is either an
               empty string or the matching history-gabby type, and the third
               being the complete command line to be added.  The entry will not
               be added to history if the hook uses a non-0 return.  [v15
               behaviour may differ] A future version will give the expanded
               command name as the third argument, followed by the tokenized
               command line as parsed in the remaining arguments, the first of
               which is the original unexpanded command name; i.e., one may do
               ‘shift 4’ and will then be able to access the positional
               parameters as usual via *, #, 1 etc.

     on-main-loop-tick
               This hook will be called whenever the program's main event loop
               is about to read the next input line.  Note variable and other
               changes it performs are not scoped as via localopts!

     on-program-exit
               This hook will be called when the program exits, whether via exit
               or quit, or because the send mode is done.

     on-resend-cleanup
               [v15 behaviour may differ] Identical to on-compose-cleanup, but
               is only triggered by resend.

     on-resend-enter
               [v15 behaviour may differ] Identical to on-compose-enter, but is
               only triggered by resend; currently there is no digmsg support,
               for example.

     page      (Boolean) If set, each message feed through the command given for
               pipe is followed by a formfeed character ‘\f’.

     password-USER@HOST, password-HOST, password
               [v15-compat] Variable chain that sets a password, which is used
               in case none has been given in the protocol and account-specific
               URL; as a last resort Mail will ask for a password on the user's
               terminal if the authentication method requires a password.
               Specifying passwords in a startup file is generally a security
               risk; the file should be readable by the invoking user only.

     password-USER@HOST
               [no v15-compat] (see the chain above for [v15-compat]) Set the
               password for ‘USER’ when connecting to ‘HOST’.  If no such
               variable is defined for a host, the user will be asked for a
               password on standard input.  Specifying passwords in a startup
               file is generally a security risk; the file should be readable by
               the invoking user only.

     piperaw   (Boolean) Send messages to the pipe command without performing
               MIME and character set conversions.

     pipe-TYPE/SUBTYPE
               When a MIME message part of type ‘TYPE/SUBTYPE’ (case-
               insensitive) is displayed or quoted, its text is filtered through
               the value of this variable interpreted as a shell command.  Note
               that only parts which can be displayed inline as plain text (see
               copiousoutput) are displayed unless otherwise noted, other MIME
               parts will only be considered by and for the command mimeview.

               The special value question mark ‘?’ forces interpretation of the
               message part as plain text, for example ‘set
               pipe-application/xml=?’ will henceforth display XML “as is”.
               (The same could also be achieved by adding a MIME type marker
               with the mimetype command.  And [Option]ally MIME type handlers
               may be defined via The Mailcap files — these directives,
               copiousoutput has already been used, should be referred to for
               further documentation.

               The question mark ‘?’ can in fact be used as a trigger character
               to adjust usage and behaviour of a following shell command
               specification more thoroughly by appending more special
               characters which refer to further mailcap directives, for example
               the following hypothetical command specification could be used:

                     ? set pipe-X/Y='?!++=? vim ${MAILX_FILENAME_TEMPORARY}'

               ‘*’       The command produces plain text to be integrated in
                         Mails output: copiousoutput.
               ‘#’       If set the handler will not be invoked when a message
                         is to be quoted, but only when it will be displayed:
                         x-mailx-noquote.
               ‘&’       Run the command asynchronously, i.e., without blocking
                         Mail: x-mailx-async.  The standard output of the
                         command will go to /dev/null.
               ‘!’       The command must be run on an interactive terminal,
                         Mail will temporarily release the terminal to it:
                         needsterminal.
               ‘+’       Request creation of a zero-sized temporary file, the
                         absolute pathname of which will be made accessible via
                         the environment variable MAILX_FILENAME_TEMPORARY:
                         x-mailx-tmpfile.  If given twice then the file will be
                         unlinked automatically by Mail when the command loop is
                         entered again at latest: x-mailx-tmpfile-unlink; it is
                         an error to use automatic deletion in conjunction with
                         x-mailx-async.
               ‘=’       Normally the MIME part content is passed to the handler
                         via standard input; if this flag is set then the data
                         will instead be written into MAILX_FILENAME_TEMPORARY
                         (x-mailx-tmpfile-fill), the creation of which is
                         implied; in order to cause automatic deletion of the
                         temporary file two plus signs ‘++’ still have to be
                         used.
               ‘?’       To avoid ambiguities with normal shell command content
                         another question mark can be used to forcefully
                         terminate interpretation of remaining characters.  (Any
                         character not in this list will have the same effect.)

               Some information about the MIME part to be displayed is embedded
               into the environment of the shell command:

               MAILX_CONTENT            The MIME content-type of the part, if
                                        known, the empty string otherwise.
               MAILX_CONTENT_EVIDENCE   If mime-counter-evidence includes the
                                        carry-around-bit (2), then this will be
                                        set to the detected MIME content-type;
                                        not only then identical to MAILX_CONTENT
                                        otherwise.
               MAILX_EXTERNAL_BODY_URL  MIME parts of type
                                        ‘message/external-body access-type=url’
                                        will store the access URL in this
                                        variable, it is empty otherwise.  URL
                                        targets should not be activated
                                        automatically, without supervision.
               MAILX_FILENAME           The filename, if any is set, the empty
                                        string otherwise.
               MAILX_FILENAME_GENERATED
                                        A random string.
               MAILX_FILENAME_TEMPORARY
                                        If temporary file creation has been
                                        requested through the command prefix
                                        this variable will be set and contain
                                        the absolute pathname of the temporary
                                        file.

     pipe-EXTENSION
               This is identical to pipe-TYPE/SUBTYPE except that ‘EXTENSION’
               (normalized to lowercase using character mappings of the ASCII
               charset) names a file extension, for example ‘xhtml’.  Handlers
               registered using this method take precedence.

     pop3-auth-USER@HOST, pop3-auth-HOST, pop3-auth
               [Option][v15-compat] Variable chain that sets the POP3
               authentication method.  Supported are the default ‘plain’,
               [v15-compat] ‘oauthbearer’ (see FAQ entry But, how about XOAUTH2
               / OAUTHBEARER?), as well as [v15-compat] ‘external’ and
               ‘externanon’ for TLS secured connections which pass a client
               certificate via tls-config-pairs.  There may be the [Option]al
               method [v15-compat] ‘gssapi’.  ‘externanon’ does not need any
               user credentials, ‘external’ and ‘gssapi’ need a user, the
               remains also require a password.  ‘externanon’ solely builds upon
               the credentials passed via a client certificate, and is usually
               the way to go since tested servers do not actually follow RFC
               4422, and fail if additional credentials are actually passed.
               Unless pop3-no-apop is set the ‘plain’ method will [Option]ally
               be replaced with APOP if possible (see there).

     pop3-bulk-load-USER@HOST, pop3-bulk-load-HOST, pop3-bulk-load
               (Boolean)[Option] When accessing a POP3 server Mail loads the
               headers of the messages, and only requests the message bodies on
               user request.  For the POP3 protocol this means that the message
               headers will be downloaded twice.  If this variable is set then
               Mail will download only complete messages from the given POP3
               server(s) instead.

     pop3-keepalive-USER@HOST, pop3-keepalive-HOST, pop3-keepalive
               [Option] POP3 servers close the connection after a period of
               inactivity; the standard requires this to be at least 10 minutes,
               but practical experience may vary.  Setting this variable to a
               numeric value greater than ‘0’ causes a ‘NOOP’ command to be sent
               each value seconds if no other operation is performed.

     pop3-no-apop-USER@HOST, pop3-no-apop-HOST, pop3-no-apop
               (Boolean)[Option] Unless this variable is set the MD5 based
               ‘APOP’ authentication method will be used instead of a chosen
               ‘plain’ pop3-auth when connecting to a POP3 server that
               advertises support.  The advantage of ‘APOP’ is that only a
               single packet is sent for the user/password tuple.  (Originally
               also that the password is not sent in clear text over the wire,
               but for one MD5 does not any longer offer sufficient security,
               and then today transport is almost ever TLS secured.)  Note that
               pop3-no-apop-HOST requires [v15-compat].

     pop3-use-starttls-USER@HOST, pop3-use-starttls-HOST, pop3-use-starttls
               (Boolean)[Option] Causes Mail to issue a ‘STLS’ command to make
               an unencrypted POP3 session TLS encrypted.  This functionality is
               not supported by all servers, and is not used if the session is
               already encrypted by the POP3S method.  Note that
               pop3-use-starttls-HOST requires [v15-compat].

     posix     (Boolean) This flag enables POSIX mode, which changes behaviour
               of Mail where that deviates from standardized behaviour.  It is
               automatically squared with the environment variable
               POSIXLY_CORRECT, changing the one will adjust the other.  The
               following behaviour is covered and enforced by this mechanism:

               In non-interactive mode, any error encountered while loading
                   resource files during program startup will cause a program
                   exit, whereas in interactive mode such errors will stop
                   loading of the currently loaded (stack of) file(s, i.e.,
                   recursively).  These exits can be circumvented on a per-
                   command base by using ignerr, one of the Command modifiers,
                   for each command which shall be allowed to fail.
               •   alternates will replace the list of alternate addresses
                   instead of appending to it.  In addition alternates will only
                   be honoured for any sort of message reply, and for aliases.
               The variable inserting COMMAND ESCAPES ~A, ~a, ~I and ~i will
                   expand embedded character sequences ‘\t’ horizontal tabulator
                   and ‘\n’ line feed.  [v15 behaviour may differ] For
                   compatibility reasons this step will always be performed.
               Reading in messages via ~f (COMMAND ESCAPES) will use the
                   ‘type’ not the ‘forward’ headerpick selection.
               Upon changing the active folder no summary of headers will be
                   displayed even if header is set.
               Setting ignoreeof implies the behaviour described by dot.
               The variable keep is extended to cover any empty mailbox, not
                   only empty primary system mailboxes: they will be removed
                   when they are left in empty state otherwise.

     print-alternatives
               (Boolean) When a MIME message part of type
               ‘multipart/alternative’ is displayed and it contains a subpart of
               type ‘text/plain’, other parts are normally discarded.  Setting
               this variable causes all subparts to be displayed, just as if the
               surrounding part was of type ‘multipart/mixed’.

     prompt    The string used as a prompt in interactive mode.  Whenever the
               variable is evaluated the value is treated as if specified within
               dollar-single-quotes (see Shell-style argument quoting).  This
               (post-assignment, i.e., second) expansion can be used to embed
               status information, for example ?, !, account or mailbox-display.

               In order to embed characters which should not be counted when
               calculating the visual width of the resulting string, enclose the
               characters of interest in a pair of reverse solidus escaped
               brackets: ‘\[\E[0m\]’; a slot for coloured prompts is also
               available with the [Option]al command colour.  Prompting may be
               prevented by setting this to the null string (aka ‘set
               noprompt’).

     prompt2   This string is used for secondary prompts, but is otherwise
               identical to prompt.  The default is ‘.. ’.

     quiet     (Boolean) Suppresses the printing of the version when first
               invoked.

     quote     If set messages processed by followup, reply and variants will be
               prefixed with the quoted original message, the lines of which
               prefixed by indentprefix, taking into account quote-chars and
               quote-fold.  No headers will be quoted when set without value or
               if the value is ‘noheading’, if it is ‘headers’ the ‘type’
               headerpick selection will be included in the quotation, whereas
               all headers and all MIME parts are included for ‘allheaders’.
               The quoted message will be enclosed by the expansions of
               quote-inject-head and quote-inject-tail.  Also see quote-add-cc,
               quote-as-attachment and ~Q, one of the COMMAND ESCAPES.

     quote-add-cc
               (Boolean) Whether the sender of a message quoted via ~Q shall be
               added to the messages' ‘Cc:’ list.

     quote-as-attachment
               (Boolean) Add the original message in its entirety as a
               ‘message/rfc822’ MIME attachment when replying to a message.
               Note this works regardless of the setting of quote.

     quote-chars
               Can be set to a string consisting of non-whitespace ASCII
               characters which shall be treated as quotation leaders, the
               default being ‘>|}:’.

     quote-fold
               [Option] Can be set in addition to indentprefix, and creates a
               more fancy quotation in that leading quotation characters
               (quote-chars) are compressed and overlong lines are folded.
               quote-fold can be set to either one, two or three (space
               separated) numeric values, which are interpreted as the maximum
               (goal) and the minimum line length, respectively, in a spirit
               rather equal to the fmt(1) program, but line- instead of
               paragraph-based.  The third value is used as the maximum line
               length instead of the first if no better break point can be
               found; it is ignored unless it is larger than the minimum and
               smaller than the maximum.  If not set explicitly the minimum will
               reflect the goal algorithmically.  The goal cannot be smaller
               than the length of indentprefix plus some additional pad;
               necessary adjustments take place silently.

     quote-inject-head, quote-inject-tail
               The strings to put before and after the text of a quoted message,
               if non-empty, and respectively.  The former defaults to ‘%f
               wrote:\n\n’.  Special format directives will be expanded if
               possible, and if so configured the output will be folded
               according to quote-fold.  Format specifiers in the given strings
               start with a percent sign ‘%’ and expand values of the original
               message, unless noted otherwise.  Note that names and addresses
               are not subject to the setting of showto.  Valid format
               specifiers are:

               ‘%%’      A plain percent sign.
               ‘%a’      The address(es) of the sender(s).
               ‘%d’      The date found in the ‘Date:’ header of the message
                         when datefield is set (the default), otherwise the date
                         when the message was received.  Formatting can be
                         controlled by assigning a strftime(3) format string to
                         datefield (and datefield-markout-older).
               ‘%f’      The full name(s) (name and address, as given) of the
                         sender(s).
               ‘%i’      The ‘Message-ID:’.
               ‘%n’      The real name(s) of the sender(s) if there is one and
                         showname allows usage, the address(es) otherwise.
               ‘%r’      The senders real name(s) if there is one, the
                         address(es) otherwise.

     r-option-implicit
               (Boolean) Setting this option evaluates the contents of from (or,
               if that contains multiple addresses, sender) and passes the
               results onto the used (file-based) MTA as described for the -r
               option (empty argument case).

     recipients-in-cc
               (Boolean) When doing a reply, the original ‘From:’ and ‘To:’ as
               well as addressees which possibly came in via ‘Reply-To:’ and
               ‘Mail-Followup-To:’ are by default merged into the new ‘To:’.  If
               this variable is set a sensitive algorithm tries to place in
               ‘To:’ only the sender of the message being replied to, others are
               placed in ‘Cc:’.

     record    Unless this variable is defined, no copies of outgoing mail will
               be saved.  If defined it gives the pathname, subject to the usual
               Filename transformations, of a folder where all new, replied-to
               or forwarded messages are saved: when saving to this folder fails
               the message is not sent, but instead saved to DEAD.  The standard
               defines that relative (fully expanded) paths are to be
               interpreted relative to the current directory (cwd), to force
               interpretation relative to folder outfolder needs to be set in
               addition.

     record-files
               (Boolean) If this variable is set the meaning of record will be
               extended to cover messages which target only file and pipe
               recipients (see expandaddr).  These address types will not appear
               in recipient lists unless add-file-recipients is also set.

     record-resent
               (Boolean) If this variable is set the meaning of record will be
               extended to also cover the resend and Resend commands.

     reply-in-same-charset
               (Boolean) If this variable is set Mail first tries to use the
               same character set of the original message for replies.  If this
               fails, the mechanism described in Character sets is evaluated as
               usual.

     reply-strings
               Can be set to a comma-separated list of (case-insensitive
               according to ASCII rules) strings which shall be recognized in
               addition to the built-in strings as ‘Subject:’ reply message
               indicators – built-in are ‘Re:’, which is mandated by RFC 5322,
               as well as the german ‘Aw:’, ‘Antw:’, and the ‘Wg:’ which often
               has been seen in the wild; I.e., the separating colon has to be
               specified explicitly.

     reply-to  A list of addresses to put into the ‘Reply-To:’ field of the
               message header.  Members of this list are handled as if they were
               in the alternates list.

     replyto   [Obsolete] Variant of reply-to.

     reply-to-honour
               Controls whether a ‘Reply-To:’ header is honoured when replying
               to a message via reply or Lreply.  This is a quadoption; if set
               without a value it defaults to “yes”.

     reply-to-swap-in
               Standards like DKIM and (in conjunction with) DMARC caused many
               Mailing lists to use sender address rewriting in the style of
               ‘Name via List <list@address>’, where the original sender address
               often being placed in ‘Reply-To:’.  If this is set and a
               ‘Reply-To:’ exists then that is used in place of the pretended
               sender.  This works independently from reply-to-honour.  The
               optional value, a comma-separated list of strings, offers more
               fine-grained control on when swapping shall be used; for now
               supported is mlist, here swapping occurs if the sender is a
               mailing-list as defined by mlist.

     rfc822-body-from_
               (Boolean) This variable can be used to force displaying a so-
               called ‘From_’ line for messages that are embedded into an
               envelope mail via the ‘message/rfc822’ MIME mechanism, for more
               visual convenience, also see mbox-rfc4155.

     save      (Boolean) Enable saving of (partial) messages in DEAD upon
               interrupt or delivery error.

     screen    The number of lines that represents a “screenful” of lines, used
               in headers summary display, from searching, message topline
               display and scrolling via z.  If this variable is not set Mail
               falls back to a calculation based upon the detected terminal
               window size and the baud rate: the faster the terminal, the more
               will be shown.  Overall screen dimensions and pager usage is
               influenced by the environment variables COLUMNS and LINES and the
               variable crt.

     searchheaders
               (Boolean) Expand message list specifiers in the form ‘/x:y’ to
               all messages containing the substring “y” in the header field
               ‘x’.  The string search is case insensitive.

     sendcharsets
               [Option] A comma-separated list of character set names that can
               be used in outgoing internet mail.  The value of the variable
               charset-8bit is automatically appended to this list of character
               sets.  If no character set conversion capabilities are compiled
               into Mail then the only supported charset is ttycharset.  Also
               see sendcharsets-else-ttycharset and refer to the section
               Character sets for the complete picture of character set
               conversion in Mail.

     sendcharsets-else-ttycharset
               (Boolean)[Option] If this variable is set, but sendcharsets is
               not, then Mail acts as if sendcharsets had been set to the value
               of the variable ttycharset.  In effect this combination passes
               through the message data in the character set of the current
               locale encoding: therefore mail message text will be (assumed to
               be) in ISO-8859-1 encoding when send from within a ISO-8859-1
               locale, and in UTF-8 encoding when send from within an UTF-8
               locale.

               The 8-bit fallback charset-8bit never comes into play as
               ttycharset is implicitly assumed to be 8-bit and capable to
               represent all files the user may specify (as is the case when no
               character set conversion support is available in Mail and the
               only supported character set is ttycharset, see Character sets).
               This might be a problem for scripts which use the suggested
               ‘LC_ALL=C’ setting, since in this case the character set is US-
               ASCII by definition, so that it is better to also override
               ttycharset, then; and/or do something like the following in the
               resource file:

                     if [ "$LC_ALL" == C ] || [ "$LC_CTYPE" == C ]
                       unset sendcharsets-else-ttycharset
                     end

     sender    An address that is put into the ‘Sender:’ field of outgoing
               messages, quoting RFC 5322: the mailbox of the agent responsible
               for the actual transmission of the message.  This field should
               normally not be used unless the from field contains more than one
               address, on which case it is required.  [v15 behaviour may
               differ] Please expect automatic management of the from and sender
               relationship.  Dependent on the context this address is handled
               as if it were in the list of alternates.  Also see -r,
               r-option-implicit.

     sendmail  [Obsolete] Predecessor of mta.

     sendmail-arguments
               [Obsolete] Predecessor of mta-arguments.

     sendmail-no-default-arguments
               [Obsolete](Boolean) Predecessor of mta-no-default-arguments.

     sendmail-progname
               [Obsolete] Predecessor of mta-argv0.

     sendwait  Sending messages to the chosen mta or to command-pipe receivers
               (see On sending mail, and non-interactive mode) will be performed
               asynchronously.  This means that only startup errors of the
               respective program will be recognizable, but no delivery errors.
               Also, no guarantees can be made as to when the respective program
               will actually run, as well as to when they will have produced
               output.

               If this variable is set then child program exit is waited for,
               and its exit status code is used to decide about success.
               Remarks: in conflict with the POSIX standard this variable is
               built-in to be initially set.  Another difference is that it can
               have a value, which is interpreted as a comma-separated list of
               case-insensitive strings naming specific subsystems for which
               synchronousness shall be ensured (only).  Possible values are
               ‘mta’ for mta delivery, and ‘pcc’ for command-pipe receivers.

     showlast  (Boolean) This setting causes Mail to start at the last message
               instead of the first one when opening a mail folder, as well as
               with from and headers.

     showname  (Boolean) Causes Mail to use the sender's real name instead of
               the plain address in the header field summary and in message
               specifications.

     showto    (Boolean) Causes the recipient of the message to be shown in the
               header summary if the message was sent by the user.

     Sign      The value backing ~A, one of the COMMAND ESCAPES.  Also see
               message-inject-tail, on-compose-leave and on-compose-splice.

     sign      The value backing ~a, one of the COMMAND ESCAPES.  Also see
               message-inject-tail, on-compose-leave and on-compose-splice.

     signature
               [Obsolete] Please use on-compose-splice or
               on-compose-splice-shell or on-compose-leave and (if necessary)
               message-inject-tail instead!

     skipemptybody
               (Boolean) If an outgoing message does not contain any text in its
               first or only message part, do not send it but discard it
               silently (see also the command line option -E).

     smime-ca-dir, smime-ca-file
               [Option] Specify the location of trusted CA certificates in PEM
               (Privacy Enhanced Mail) for the purpose of verification of S/MIME
               signed messages.  tls-ca-dir documents the necessary preparation
               steps to use the former.  The set of CA certificates which are
               built into the TLS library can be explicitly turned off by
               setting smime-ca-no-defaults, and further fine-tuning is possible
               via smime-ca-flags.

     smime-ca-flags
               [Option] Can be used to fine-tune behaviour of the X509 CA
               certificate storage, and the certificate verification that is
               used.  The actual values and their meanings are documented for
               tls-ca-flags.

     smime-ca-no-defaults
               (Boolean)[Option] Do not load the default CA locations that are
               built into the used to TLS library to verify S/MIME signed
               messages.

     smime-cipher-USER@HOST, smime-cipher
               [Option] Specifies the cipher to use when generating S/MIME
               encrypted messages (for the specified account).  RFC 5751
               mandates a default of ‘aes128’ (AES-128 CBC).  Possible values
               are (case-insensitive and) in decreasing cipher strength:
               ‘aes256’ (AES-256 CBC), ‘aes192’ (AES-192 CBC), ‘aes128’ (AES-128
               CBC), ‘des3’ (DES EDE3 CBC, 168 bits; default if ‘aes128’ is not
               available) and ‘des’ (DES CBC, 56 bits).

               The actually available cipher algorithms depend on the
               cryptographic library that Mail uses.  [Option] Support for more
               cipher algorithms may be available through dynamic loading via
               EVP_get_cipherbyname(3) (OpenSSL) if Mail has been compiled to
               support this.

     smime-crl-dir
               [Option] Specifies a directory that contains files with CRLs in
               PEM format to use when verifying S/MIME messages.

     smime-crl-file
               [Option] Specifies a file that contains a CRL in PEM format to
               use when verifying S/MIME messages.

     smime-encrypt-USER@HOST
               [Option] If this variable is set, messages send to the given
               receiver are encrypted before sending.  The value of the variable
               must be set to the name of a file that contains a certificate in
               PEM format.

               If a message is sent to multiple recipients, each of them for
               whom a corresponding variable is set will receive an individually
               encrypted message; other recipients will continue to receive the
               message in plain text unless the smime-force-encryption variable
               is set.  It is recommended to sign encrypted messages, i.e., to
               also set the smime-sign variable.
               content-description-smime-message will be inspected for messages
               which become encrypted.

     smime-force-encryption
               (Boolean)[Option] Causes Mail to refuse sending unencrypted
               messages.

     smime-sign
               (Boolean)[Option] S/MIME sign outgoing messages with the user's
               (from) private key and include the users certificate as a MIME
               attachment.  Signing a message enables a recipient to verify that
               the sender used a valid certificate, that the email addresses in
               the certificate match those in the message header and that the
               message content has not been altered.  It does not change the
               message text, and people will be able to read the message as
               usual.  content-description-smime-signature will be inspected.
               Also see smime-sign-cert, smime-sign-include-certs and
               smime-sign-digest.

     smime-sign-cert-USER@HOST, smime-sign-cert
               [Option] Points to a file in PEM format.  For the purpose of
               signing and decryption this file needs to contain the user's
               private key, followed by his certificate.

               For message signing ‘USER@HOST’ is always derived from the value
               of from (or, if that contains multiple addresses, sender).  For
               the purpose of encryption the recipients public encryption key
               (certificate) is expected; the command certsave can be used to
               save certificates of signed messages (the section Signed and
               encrypted messages with S/MIME gives some details).  This mode of
               operation is usually driven by the specialized form.

               When decrypting messages the account is derived from the
               recipient fields (‘To:’ and ‘Cc:’) of the message, which are
               searched for addresses for which such a variable is set.  Mail
               always uses the first address that matches, so if the same
               message is sent to more than one of the user addresses using
               different encryption keys, decryption might fail.

               Password-encrypted keys may be used for signing and decryption.
               Automated password lookup is possible via the “pseudo-hosts”
               ‘USER@HOST.smime-cert-key’ for the private key, and
               ‘USER@HOST.smime-cert-cert’ for the certificate stored in the
               same file.  For example, the hypothetical address ‘bob@exam.ple’
               could be driven with a private key / certificate pair path
               defined in smime-sign-cert-bob@exam.ple, and the needed passwords
               would then be looked up as ‘bob@exam.ple.smime-cert-key’ and
               ‘bob@exam.ple.smime-cert-cert’.  When decrypting the value of
               from will be tried as a fallback to provide the necessary
               ‘USER@HOST’.  To include intermediate certificates, use
               smime-sign-include-certs.  The possible password sources are
               documented in On URL syntax and credential lookup.

     smime-sign-digest-USER@HOST, smime-sign-digest
               [Option] Specifies the message digest to use when signing S/MIME
               messages.  Please remember that for this use case ‘USER@HOST’
               refers to the variable from (or, if that contains multiple
               addresses, sender).  The available algorithms depend on the used
               cryptographic library, but at least one usable built-in algorithm
               is ensured as a default.  If possible the standard RFC 5751 will
               be violated by using ‘SHA512’ instead of the mandated ‘SHA1’ due
               to security concerns.

               Mail will try to add built-in support for the following message
               digests, names are case-insensitive: ‘BLAKE2b512’, ‘BLAKE2s256’,
               ‘SHA3-512’, ‘SHA3-384’, ‘SHA3-256’, ‘SHA3-224’, as well as the
               widely available ‘SHA512’, ‘SHA384’, ‘SHA256’, ‘SHA224’, and the
               proposed insecure ‘SHA1’, finally ‘MD5’.  More digests may
               [Option]ally be available through dynamic loading via the OpenSSL
               function EVP_get_digestbyname(3).

     smime-sign-include-certs-USER@HOST, smime-sign-include-certs
               [Option] If used, this is supposed to a consist of a comma-
               separated list of files, each of which containing a single
               certificate in PEM format to be included in the S/MIME message in
               addition to the smime-sign-cert certificate.  This can be used to
               include intermediate certificates of the certificate authority,
               in order to allow the receiver's S/MIME implementation to perform
               a verification of the entire certificate chain, starting from a
               local root certificate, over the intermediate certificates, down
               to the smime-sign-cert.  Even though top level certificates may
               also be included in the chain, they will not be used for the
               verification on the receiver's side.

               For the purpose of the mechanisms involved here, ‘USER@HOST’
               refers to the content of the internal variable from (or, if that
               contains multiple addresses, sender).  The pseudo-host
               ‘USER@HOST.smime-include-certs’ will be used for performing
               password lookups for these certificates, shall they have been
               given one, therefore the lookup can be automated via the
               mechanisms described in On URL syntax and credential lookup.

     smime-sign-message-digest-USER@HOST, smime-sign-message-digest
               [Obsolete][Option] Predecessor(s) of smime-sign-digest.

     smtp      [Obsolete][Option] To use the built-in SMTP transport, specify a
               SMTP URL in mta.  [v15 behaviour may differ] For compatibility
               reasons a set smtp is used in preference of mta.

     smtp-auth-USER@HOST, smtp-auth-HOST, smtp-auth
               [Option] Variable chain that controls the SMTP mta authentication
               method, possible values are ‘none’ ([no v15-compat] default),
               ‘plain’ ([v15-compat] default), ‘login’, [v15-compat]
               ‘oauthbearer’ (see FAQ entry But, how about XOAUTH2 /
               OAUTHBEARER?) as well as [v15-compat] ‘external’ and ‘externanon’
               for TLS secured connections which pass a client certificate via
               tls-config-pairs.  There may be the [Option]al methods ‘cram-md5’
               and ‘gssapi’.  ‘none’ and ‘externanon’ do not need any user
               credentials, ‘external’ and ‘gssapi’ require a user name, and all
               other methods require a user name and a password.  ‘externanon’
               solely builds upon the credentials passed via a client
               certificate, and is usually the way to go since tested servers do
               not actually follow RFC 4422 aka RFC 4954, and fail if additional
               credentials are passed.  Also see mta.  Note that smtp-auth-HOST
               is [v15-compat].  ([no v15-compat] Requires smtp-auth-password
               and smtp-auth-user.  Note for smtp-auth-USER@HOST: may override
               dependent on sender address in the variable from.)

     smtp-auth-password
               [Option][no v15-compat] Sets the global fallback password for
               SMTP authentication.  If the authentication method requires a
               password, but neither smtp-auth-password nor a matching
               smtp-auth-password-USER@HOST can be found, Mail will ask for a
               password on the user's terminal.

     smtp-auth-password-USER@HOST
               [no v15-compat] Overrides smtp-auth-password for specific values
               of sender addresses, dependent upon the variable from.

     smtp-auth-user
               [Option][no v15-compat] Sets the global fallback user name for
               SMTP authentication.  If the authentication method requires a
               user name, but neither smtp-auth-user nor a matching
               smtp-auth-user-USER@HOST can be found, Mail will ask for a user
               name on the user's terminal.

     smtp-auth-user-USER@HOST
               [no v15-compat] Overrides smtp-auth-user for specific values of
               sender addresses, dependent upon the variable from.

     smtp-hostname
               [Option][v15-compat] Normally Mail uses the variable from to
               derive the necessary ‘USER@HOST’ information in order to issue a
               ‘MAIL FROM:<>’ SMTP mta command.  Setting smtp-hostname can be
               used to use the ‘USER’ from the SMTP account (mta or the user
               variable chain) and the given ‘HOST’ (hostname if the empty
               string is given, or the local hostname as a last resort).  This
               often allows using an address that is itself valid but hosted by
               a provider other than from which (in from) the message is sent.
               Setting this variable also influences generated ‘Message-ID:’ and
               ‘Content-ID:’ header fields.  If the [Option]al IDNA support is
               available (see idna-disable) variable assignment is aborted when
               a necessary conversion fails.

     smtp-use-starttls-USER@HOST, smtp-use-starttls-HOST, smtp-use-starttls
               (Boolean)[Option] Causes Mail to issue a ‘STARTTLS’ command to
               make an SMTP mta session TLS encrypted, i.e., to enable transport
               layer security.

     socket-connect-timeout
               [Option] A positive number that defines the timeout to wait for
               establishing a socket connection before forcing ^ERR-TIMEDOUT.

     socks-proxy-USER@HOST, socks-proxy-HOST, socks-proxy
               [Option] If set to the URL of a SOCKS5 server then all network
               activities are proxied through it, except for the single DNS name
               lookup necessary to resolve the proxy URL (unnecessary when given
               an already resolved IP address).  It is automatically squared
               with the environment variable SOCKS5_PROXY, changing the one will
               adjust the other.  This example creates a local SOCKS5 proxy on
               port 10000 that forwards to the machine ‘HOST’ (with identity
               ‘USER’), and from which actual network traffic happens:

                     $ ssh -D 10000 USER@HOST
                     $ mail -Ssocks-proxy=[socks5://]localhost:10000
                     # or =localhost:10000; no local DNS: =127.0.0.1:10000

     spam-interface
               [Option] In order to use any of the spam-related commands (like
               spamrate) the desired spam interface must be defined by setting
               this variable.  Please refer to the manual section Handling spam
               for the complete picture of spam handling in Mail.  All or none
               of the following interfaces may be available:

               ‘spamc’   Interaction with spamc(1) from the spamassassin(1)
                         (SpamAssassin: http://spamassassin.apache.org) suite.
                         Different to the generic filter interface Mail will
                         automatically add the correct arguments for a given
                         command and has the necessary knowledge to parse the
                         program's output.  A default value for spamc-command
                         will have been compiled into the Mail binary if
                         spamc(1) has been found in PATH during compilation.
                         Shall it be necessary to define a specific connection
                         type (rather than using a configuration file for that),
                         the variable spamc-arguments can be used as in for
                         example ‘-d server.example.com -p 783’.  It is also
                         possible to specify a per-user configuration via
                         spamc-user.  Note that this interface does not inspect
                         the ‘is-spam’ flag of a message for the command
                         spamforget.

               ‘filter’  generic spam filter support via freely configurable
                         hooks.  This interface is meant for programs like
                         bogofilter(1) and requires according behaviour in
                         respect to the hooks' exit status for at least the
                         command spamrate (‘0’ meaning a message is spam, ‘1’
                         for non-spam, ‘2’ for unsure and any other return value
                         indicating a hard error); since the hooks can include
                         shell code snippets diverting behaviour can be
                         intercepted as necessary.  The hooks are
                         spamfilter-ham, spamfilter-noham, spamfilter-nospam,
                         spamfilter-rate and spamfilter-spam; the manual section
                         Handling spam contains examples for some programs.  The
                         process environment of the hooks will have the variable
                         MAILX_FILENAME_GENERATED set.  Note that spam score
                         support for spamrate is not supported unless the
                         [Option]tional regular expression support is available
                         and the spamfilter-rate-scanscore variable is set.

     spam-maxsize
               [Option] Messages that exceed this size will not be passed
               through to the configured spam-interface.  If unset or 0, the
               default of 420000 bytes is used.

     spamc-command
               [Option] The path to the spamc(1) program for the ‘spamc’
               spam-interface.  Note that the path is not expanded, but used “as
               is”.  A fallback path will have been compiled into the Mail
               binary if the executable had been found during compilation.

     spamc-arguments
               [Option] Even though Mail deals with most arguments for the
               ‘spamc’ spam-interface automatically, it may at least sometimes
               be desirable to specify connection-related ones via this
               variable, for example ‘-d server.example.com -p 783’.

     spamc-user
               [Option] Specify a username for per-user configuration files for
               the ‘spamc’ spam-interface.  If this is set to the empty string
               then Mail will use the name of the current user.

     spamfilter-ham, spamfilter-noham, spamfilter-nospam, spamfilter-rate,
               spamfilter-spam
               [Option] Command and argument hooks for the ‘filter’
               spam-interface.  The manual section Handling spam contains
               examples for some programs.

     spamfilter-rate-scanscore
               [Option] Because of the generic nature of the ‘filter’
               spam-interface spam scores are not supported for it by default,
               but if the [Option]nal regular expression support is available
               then setting this variable can be used to overcome this
               restriction.  It is interpreted as follows: first a number
               (digits) is parsed that must be followed by a semicolon ‘;’ and
               an extended regular expression.  Then the latter is used to parse
               the first output line of the spamfilter-rate hook, and, in case
               the evaluation is successful, the group that has been specified
               via the number is interpreted as a floating point scan score.

     ssl-ca-dir-USER@HOST, ssl-ca-dir-HOST, ssl-ca-dir, ssl-ca-file-USER@HOST,
               ssl-ca-file-HOST, ssl-ca-file
               [Obsolete][Option] Predecessors of tls-ca-file, tls-ca-dir.

     ssl-ca-flags-USER@HOST, ssl-ca-flags-HOST, ssl-ca-flags
               [Obsolete][Option] Predecessor of tls-ca-flags.

     ssl-ca-no-defaults-USER@HOST, ssl-ca-no-defaults-HOST, ssl-ca-no-defaults
               [Obsolete](Boolean)[Option] Predecessor of tls-ca-no-defaults.

     ssl-cert-USER@HOST, ssl-cert-HOST, ssl-cert
               [Obsolete][Option] Please use the Certificate slot of
               tls-config-pairs.

     ssl-cipher-list-USER@HOST, ssl-cipher-list-HOST, ssl-cipher-list
               [Obsolete][Option] Please use the CipherString slot of
               tls-config-pairs.

     ssl-config-file
               [Obsolete][Option] Predecessor of tls-config-file.

     ssl-config-module-USER@HOST, ssl-config-module-HOST, ssl-config-module
               [Obsolete][Option] Predecessor of tls-config-module.

     ssl-config-pairs-USER@HOST, ssl-config-pairs-HOST, ssl-config-pairs
               [Obsolete][Option] Predecessor of tls-config-pairs.

     ssl-crl-dir, ssl-crl-file
               [Obsolete][Option] Predecessors of tls-crl-dir, tls-crl-file.

     ssl-curves-USER@HOST, ssl-curves-HOST, ssl-curves
               [Obsolete][Option] Please use the Curves slot of
               tls-config-pairs.

     ssl-features
               [Obsolete][Option](Read-only) Predecessor of tls-features.

     ssl-key-USER@HOST, ssl-key-HOST, ssl-key
               [Obsolete][Option] Please use the PrivateKey slot of
               tls-config-pairs.

     ssl-method-USER@HOST, ssl-method-HOST, ssl-method
               [Obsolete][Option] Please use the Protocol slot of
               tls-config-pairs.

     ssl-protocol-USER@HOST, ssl-protocol-HOST, ssl-protocol
               [Obsolete][Option] Please use the Protocol slot of
               tls-config-pairs.

     ssl-rand-file
               [Obsolete][Option] Predecessor of tls-rand-file.

     ssl-verify-USER@HOST, ssl-verify-HOST, ssl-verify
               [Obsolete][Option] Predecessor of tls-verify.

     stealthmua
               If only set without an assigned value, then this setting inhibits
               the generation of the ‘Message-ID:’, ‘Content-ID:’ and
               ‘User-Agent:’ header fields that include obvious references to
               Mail.  There are two pitfalls associated with this: First, the
               message id of outgoing messages is not known anymore.  Second, an
               expert may still use the remaining information in the header to
               track down the originating mail user agent.  If set to the value
               ‘noagent’, then the mentioned ‘Message-ID:’ and ‘Content-ID:’
               suppression does not occur.

     system-mailrc
               (Read-only) The compiled in path of the system wide
               initialization file one of the Resource files: mail.rc.

     termcap   ([Option]) This specifies a comma-separated list of Terminal
               Information Library (libterminfo, -lterminfo) and/or Termcap
               Access Library (libtermcap, -ltermcap) capabilities (see On
               terminal control and line editor, escape commas with reverse
               solidus) to be used to overwrite or define entries.  Note this
               variable will only be queried once at program startup and can
               thus only be specified in resource files or on the command line.

               String capabilities form ‘cap=value’ pairs and are expected
               unless noted otherwise.  Numerics have to be notated as
               ‘cap#number’ where the number is expected in normal decimal
               notation.  Finally, booleans do not have any value but indicate a
               true or false state simply by being defined or not; this indeed
               means that Mail does not support undefining an existing boolean.
               String capability values will undergo some expansions before use:
               for one notations like ‘^LETTER’ stand for ‘control-LETTER’, and
               for clarification purposes ‘\E’ can be used to specify ‘escape’
               (the control notation ‘^[’ could lead to misreadings when a left
               bracket follows, which it does for the standard CSI sequence);
               finally three letter octal sequences, as in ‘\061’, are
               supported.  To specify that a terminal supports 256-colours, and
               to define sequences that home the cursor and produce an audible
               bell, one might write:

                     ? set termcap='Co#256,home=\E[H,bel=^G'

               The following terminal capabilities are or may be meaningful for
               the operation of the built-in line editor or Mail in general:

               am        auto_right_margin: boolean which indicates if the right
                         margin needs special treatment; the xenl capability is
                         related, for more see COLUMNS.
               clear or cl
                         clear_screen: clear the screen and home cursor.  (Will
                         be simulated via ho plus cd.)
               colors or Co
                         max_colors: numeric capability specifying the maximum
                         number of colours.  Note that Mail does not actually
                         care about the terminal beside that, but always emits
                         ANSI / ISO 6429 escape sequences; also see colour.
               cr        carriage_return: move to the first column in the
                         current row.  The default built-in fallback is ‘\r’.
               cub1 or le
                         cursor_left: move the cursor left one space (non-
                         destructively).  The default built-in fallback is ‘\b’.
               cuf1 or nd
                         cursor_right: move the cursor right one space (non-
                         destructively).  The default built-in fallback is
                         ‘\E[C’, which is used by most terminals.  Less often
                         occur ‘\EC’ and ‘\EOC’.
               ed or cd  clr_eos: clear the screen.
               el or ce  clr_eol: clear to the end of line.  (Will be simulated
                         via ch plus repetitions of space characters.)
               home or ho
                         cursor_home: home cursor.
               hpa or ch
                         column_address: move the cursor (to the given column
                         parameter) in the current row.  (Will be simulated via
                         cr plus nd.)
               rmcup or te / smcup or ti
                         exit_ca_mode and enter_ca_mode, respectively: exit and
                         enter the alternative screen ca-mode, effectively
                         turning Mail into a fullscreen application.  This must
                         be enabled explicitly by setting termcap-ca-mode.
               smkx or ks / rmkx or ke
                         keypad_xmit and keypad_local, respectively: enable and
                         disable the keypad.  This is always enabled if
                         available, because it seems even keyboards without
                         keypads generate other key codes for, e.g., cursor keys
                         in that case, and only if enabled we see the codes that
                         we are interested in.
               xenl or xn
                         eat_newline_glitch: boolean which indicates whether a
                         newline written in the last column of an
                         auto_right_margin indicating terminal is ignored.  With
                         it the full terminal width is available even on
                         autowrap terminals.

               Many more capabilities which describe key-sequences are
               documented for bind.

     termcap-ca-mode
               [Option] Allow usage of the exit_ca_mode and enter_ca_mode
               termcapabilities in order to enter an alternative exclusive
               screen, the so-called ca-mode; this usually requires special
               configuration of the PAGER, also dependent on the value of crt.
               Note this variable will only be queried once at program startup
               and can thus only be specified in resource files or on the
               command line.

     termcap-disable
               [Option] Disable any interaction with a terminal control library.
               If set only some generic fallback built-ins and possibly the
               content of termcap describe the terminal to Mail.  Note this
               variable will only be queried once at program startup and can
               thus only be specified in resource files or on the command line.

     tls-ca-dir-USER@HOST, tls-ca-dir-HOST, tls-ca-dir, tls-ca-file-USER@HOST,
               tls-ca-file-HOST, tls-ca-file
               [Option] Directory and file, respectively, for pools of trusted
               CA certificates in PEM (Privacy Enhanced Mail) format, for the
               purpose of verification of TLS server certificates.  Concurrent
               use is possible, the file is loaded once needed first, the
               directory lookup is performed anew as a last resort whenever
               necessary.  The CA certificate pool built into the TLS library
               can be disabled via tls-ca-no-defaults, further fine-tuning is
               possible via tls-ca-flags.  The directory search requires special
               filename conventions, please see SSL_CTX_load_verify_locations(3)
               and verify(1) (or c_rehash(1)).

     tls-ca-flags-USER@HOST, tls-ca-flags-HOST, tls-ca-flags
               [Option] Can be used to fine-tune behaviour of the X509 CA
               certificate storage, and the certificate verification that is
               used (also see tls-verify).  The value is expected to consist of
               a comma-separated list of configuration directives, with any
               intervening whitespace being ignored.  The directives directly
               map to flags that can be passed to X509_STORE_set_flags(3), which
               are usually defined in a file openssl/x509_vfy.h, and the
               availability of which depends on the used TLS library version: a
               directive without mapping is ignored (error log subject to
               debug).  Directives currently understood (case-insensitively)
               include:

               no-alt-chains
                         If the initial chain is not trusted, do not attempt to
                         build an alternative chain.  Setting this flag will
                         make OpenSSL certificate verification match that of
                         older OpenSSL versions, before automatic building and
                         checking of alternative chains has been implemented;
                         also see trusted-first.
               no-check-time
                         Do not check certificate/CRL validity against current
                         time.
               partial-chain
                         By default partial, incomplete chains which cannot be
                         verified up to the chain top, a self-signed root
                         certificate, will not verify.  With this flag set, a
                         chain succeeds to verify if at least one signing
                         certificate of the chain is in any of the configured
                         trusted stores of CA certificates.  The OpenSSL manual
                         page SSL_CTX_load_verify_locations(3) gives some advise
                         how to manage your own trusted store of CA
                         certificates.
               strict    Disable workarounds for broken certificates.
               trusted-first
                         Try building a chain using issuers in the trusted store
                         first to avoid problems with server-sent legacy
                         intermediate certificates.  Newer versions of OpenSSL
                         support alternative chain checking and enable it by
                         default, resulting in the same behaviour; also see
                         no-alt-chains.

     tls-ca-no-defaults-USER@HOST, tls-ca-no-defaults-HOST, tls-ca-no-defaults
               (Boolean)[Option] Do not load the default CA locations that are
               built into the used to TLS library to verify TLS server
               certificates.

     tls-config-file
               [Option] If this variable is set CONF_modules_load_file(3) (if
               announced via ‘+modules-load-file’ in tls-features) is used to
               allow resource file based configuration of the TLS library.  This
               happens once the library is used first, which may also be early
               during startup (logged with verbose)!  If a non-empty value is
               given then the given file, after performing Filename
               transformations, will be used instead of the TLS libraries global
               default, and it is an error if the file cannot be loaded.  The
               application name will always be passed as ‘mail’.  Some TLS
               libraries support application-specific configuration via resource
               files loaded like this, please see tls-config-module.

     tls-config-module-USER@HOST, tls-config-module-HOST, tls-config-module
               [Option] If file based application-specific configuration via
               tls-config-file is available, announced as ‘+ctx-config’ by
               tls-features, indicating availability of SSL_CTX_config(3), then,
               it becomes possible to use a central TLS configuration file for
               all programs, including mail, for example

                     # Register a configuration section for mail
                     mail = mailx_master
                     # The top configuration section creates a relation
                     # in between dynamic SSL configuration and an actual
                     # program specific configuration section
                     [mailx_master]
                     ssl_conf = mailx_tls_config
                     # And that program specific configuration section now
                     # can map diverse tls-config-module names to sections,
                     # as in: tls-config-module=account_xy
                     [mailx_tls_config]
                     account_xy = mailx_account_xy
                     account_yz = mailx_account_yz
                     [mailx_account_xy]
                     MinProtocol = TLSv1.2
                     Curves=P-521
                     [mailx_account_yz]
                     CipherString = TLSv1.2:!aNULL:!eNULL:
                     MinProtocol = TLSv1.1
                     Options = Bugs

     tls-config-pairs-USER@HOST, tls-config-pairs-HOST, tls-config-pairs
               [Option] The value of this variable chain will be interpreted as
               a comma-separated list of directive/value pairs.  Directives and
               values need to be separated by equals signs ‘=’, any whitespace
               surrounding pair members is removed.  Keys are (usually) case-
               insensitive.  Different to when placing these pairs in a
               tls-config-module section of a tls-config-file, commas ‘,’ need
               to be escaped with a reverse solidus ‘\’ when included in pairs;
               also different: if the equals sign ‘=’ is preceded with an
               asterisk ‘*’ Filename transformations will be performed on the
               value; it is an error if these fail.  Unless proper support is
               announced by tls-features (‘+conf-ctx’) only the keys below are
               supported, otherwise the pairs will be used directly as arguments
               to the function SSL_CONF_cmd(3).

               Certificate   Filename of a TLS client certificate (chain)
                             required by some servers.  Fallback support via
                             SSL_CTX_use_certificate_chain_file(3).  Filename
                             transformations are performed.  PrivateKey will be
                             set to the same value if not initialized
                             explicitly.  Some services support so-called
                             ‘external’ authentication if a TLS client
                             certificate was successfully presented during
                             connection establishment (“connecting is
                             authenticating”).
               CipherString  A list of ciphers for TLS connections, see
                             ciphers(1).  By default no list of ciphers is set,
                             resulting in a Protocol-specific list of ciphers
                             (the protocol standards define lists of acceptable
                             ciphers; possibly cramped by the used TLS library).
                             Fallback support via SSL_CTX_set_cipher_list(3).
               Ciphersuites  A list of ciphers used for TLSv1.3 connections, see
                             ciphers(1).  These will be joined onto the list of
                             ciphers from CipherString.  Available if
                             tls-features announces ‘+ctx-set-ciphersuites’, as
                             necessary via SSL_CTX_set_ciphersuites(3).
               Curves        A list of supported elliptic curves, if applicable.
                             By default no curves are set.  Fallback support via
                             SSL_CTX_set1_curves_list(3), if available.
               MaxProtocol, MinProtocol
                             The maximum and minimum supported TLS versions,
                             respectively.  Available if tls-features announces
                             ‘+ctx-set-maxmin-proto’, as necessary via
                             SSL_CTX_set_max_proto_version(3) and
                             SSL_CTX_set_min_proto_version(3); these fallbacks
                             use an internal parser which understands the
                             strings ‘SSLv3’, ‘TLSv1’, ‘TLSv1.1’, ‘TLSv1.2’,
                             ‘TLSv1.3’, and the special value ‘None’, which
                             disables the given limit.
               Options       Various flags to set.  Fallback via
                             SSL_CTX_set_options(3), in which case any other
                             value but (exactly) ‘Bugs’ results in an error.
               PrivateKey    Filename of the private key in PEM format of a TLS
                             client certificate.  If unset, the value of
                             Certificate is used.  Filename transformations are
                             performed.  Fallback via
                             SSL_CTX_use_PrivateKey_file(3).
               Protocol      The used TLS protocol.  If tls-features announces
                             ‘+conf-ctx’ or ‘ctx-set-maxmin-proto’ then using
                             MaxProtocol and MinProtocol is preferable.
                             Fallback is SSL_CTX_set_options(3), driven via an
                             internal parser which understands the strings
                             ‘SSLv3’, ‘TLSv1’, ‘TLSv1.1’, ‘TLSv1.2’, ‘TLSv1.3’,
                             and the special value ‘ALL’.  Multiple protocols
                             may be given as a comma-separated list, any
                             whitespace is ignored, an optional plus sign ‘+’
                             prefix enables, a hyphen-minus ‘-’ prefix disables
                             a protocol, so that ‘-ALL, TLSv1.2’ enables only
                             the TLSv1.2 protocol.

     tls-crl-dir, tls-crl-file
               [Option] Specify a directory / a file, respectively, that
               contains a CRL in PEM format to use when verifying TLS server
               certificates.

     tls-features
               [Option](Read-only) This expands to a comma-separated list of the
               TLS library identity and optional features.  To ease substring
               matching the string starts and ends with a comma.  Currently
               supported identities are ‘libressl’ (LibreSSL) , ‘libssl-0x30000’
               (OpenSSL v3.0.0 series), ‘libssl-0x10100’ (OpenSSL v1.1.x series)
               and ‘libssl-0x10000’ (elder OpenSSL series, other clones).
               Optional features are preceded with a plus sign ‘+’ when
               available, and with a hyphen-minus ‘-’ otherwise.

               Currently known features are ‘conf-ctx’ (tls-config-pairs),
               ‘ctx-config’ (tls-config-module), ‘ctx-set-ciphersuites’
               (Ciphersuites slot of tls-config-pairs), ‘ctx-set-maxmin-proto’
               (tls-config-pairs), ‘modules-load-file’ (tls-config-file), and
               ‘tls-rand-file’ (tls-rand-file).

     tls-fingerprint-USER@HOST, tls-fingerprint-HOST, tls-fingerprint
               [Option] It is possible to replace the verification of the
               connection peer certificate against the entire local pool of CAs
               (for more see Encrypted network communication) with the
               comparison against a precalculated certificate message digest,
               the so-called fingerprint, to be specified as the used
               tls-fingerprint-digest.  This fingerprint can for example be
               calculated with ‘tls fingerprint HOST’.

     tls-fingerprint-digest-USER@HOST, tls-fingerprint-digest-HOST,
               tls-fingerprint-digest
               [Option] The message digest to be used when creating TLS
               certificate fingerprints, the defaults, if available, in test
               order, being ‘BLAKE2s256’, ‘SHA256’.  For the complete list of
               digest algorithms refer to smime-sign-digest.

     tls-rand-file
               [Option] If tls-features announces ‘+tls-rand-file’ then this
               will be queried to find a file with random entropy data which can
               be used to seed the P(seudo)R(andom)N(umber)G(enerator), see
               RAND_load_file(3).  The default filename (RAND_file_name(3),
               normally ~/.rnd) will be used if this variable is not set or
               empty, or if the Filename transformations fail.  Shall seeding
               the PRNG have been successful, RAND_write_file(3) will be called
               to update the entropy.  Remarks: libraries which do not announce
               this feature seed the PRNG by other means.

     tls-verify-USER@HOST, tls-verify-HOST, tls-verify
               [Option] Variable chain that sets the action to be performed if
               an error occurs during TLS server certificate validation against
               the specified or default trust stores tls-ca-dir, tls-ca-file, or
               the TLS library built-in defaults (unless usage disallowed via
               tls-ca-no-defaults), and as fine-tuned via tls-ca-flags.  Valid
               (case-insensitive) values are ‘strict’ (fail and close connection
               immediately), ‘ask’ (ask whether to continue on standard input),
               ‘warn’ (show a warning and continue), ‘ignore’ (do not perform
               validation).  The default is ‘ask’.

     toplines  If defined, gives the number of lines of a message to be
               displayed with the command top; if unset, the first five lines
               are printed, if set to 0 the variable screen is inspected.  If
               the value is negative then its absolute value will be used for
               unsigned right shifting (see vexpr) the screen height.

     topsqueeze
               (Boolean) If set then the top command series will strip adjacent
               empty lines and quotations.

     ttycharset
               The character set of the terminal Mail operates on, and the one
               and only supported character set that Mail can use if no
               character set conversion capabilities have been compiled into it,
               in which case it defaults to ISO-8859-1.  Otherwise it defaults
               to UTF-8.  Sufficient locale support provided the default will be
               preferably deduced from the locale environment if that is set
               (for example LC_CTYPE, see there for more); runtime locale
               changes will be reflected by ttycharset except during the program
               startup phase and if -S had been used to freeze the given value.
               Refer to the section Character sets for the complete picture
               about character sets.

     typescript-mode
               (Boolean) A special multiplex variable that disables all
               variables and settings which result in behaviour that interferes
               with running Mail in script(1); it sets colour-disable,
               line-editor-disable and (before startup completed only)
               termcap-disable.  Unsetting it does not restore the former state
               of the covered settings.

     umask     For a safe-by-default policy the process file mode creation mask
               umask(2) will be set to ‘0077’ on program startup after the
               resource files have been loaded, and unless this variable is set.
               By assigning this an empty value the active setting will not be
               changed, otherwise the given value will be made the new file mode
               creation mask.  Child processes inherit the file mode creation
               mask of their parent.

     user-HOST, user
               [v15-compat] Variable chain that sets a global fallback user
               name, used in case none has been given in the protocol and
               account-specific URL.  This variable defaults to the name of the
               user who runs Mail.

     v15-compat
               Enable upward compatibility with Mail version 15.0 in respect to
               which configuration options are available and how they are
               handled.  If set to a non-empty value the command modifier wysh
               is implied and thus enforces Shell-style argument quoting over
               Old-style argument quoting for all commands which support both.
               This manual uses [v15-compat] and [no v15-compat] to refer to the
               new and the old way of doing things, respectively.

     verbose   Verbose mode enables logging of informational context messages.
               Historically a (Boolean) variable, this can either be set
               multiple times (what the command line option -v uses), or be
               assigned a numeric value in order to increase verbosity.
               Assigning the value 0 disables verbosity and thus (almost) equals
               unset.  The maximum number is 3.  Also see debug.

     version, version-date, version-hexnum, version-major, version-minor,
               version-update
               (Read-only) Mail version information: the first variable is a
               string with the complete version identification, the second the
               release date in ISO 8601 notation without time.  The third is a
               32-bit hexadecimal number with the upper 8 bits storing the
               major, followed by the minor and update version numbers which
               occupy 12 bits each.  The latter three variables contain only
               decimal digits: the major, minor and update version numbers.  The
               output of the command version will include this information.

     writebackedited
               If this variable is set messages modified using the edit or
               visual commands are written back to the current folder when it is
               quit; it is only honoured for writable folders in MBOX format,
               though.  Note that the editor will be pointed to the raw message
               content in that case, i.e., neither MIME decoding nor decryption
               will have been performed, and proper mbox-rfc4155 ‘From_’ quoting
               of newly added or edited content is also left as an exercise to
               the user.

ENVIRONMENT
     The term “environment variable” should be considered an indication that
     these variables are either standardized as vivid parts of process
     environments, or that they are commonly found in there.  The process
     environment is inherited from the sh(1) once Mail is started, and unless
     otherwise explicitly noted handling of the following variables
     transparently integrates into that of the INTERNAL VARIABLES from Mail's
     point of view.  This means they can be managed via set and unset, causing
     automatic program environment updates (to be inherited by newly created
     child processes).

     In order to integrate other environment variables equally they need to be
     imported (linked) with the command environ.  This command can also be used
     to set and unset non-integrated environment variables from scratch,
     sufficient system support provided.  The following example, applicable to a
     POSIX shell, sets the COLUMNS environment variable for Mail only, and
     beforehand exports the EDITOR in order to affect any further processing in
     the running shell:

           $ EDITOR="vim -u ${HOME}/.vimrc"
           $ export EDITOR
           $ COLUMNS=80 mail -R

     COLUMNS   The user's preferred width in column positions for the terminal
               screen.  Queried and used once on program startup in interactive
               or batch (-#) mode, actively managed for child processes and the
               MLE (see On terminal control and line editor) in interactive mode
               thereafter.  Non-interactive mode always uses, and the fallback
               default is a compile-time constant, by default 80 columns.  If in
               batch mode COLUMNS and LINES are both set but not both are usable
               (empty, not a number, or 0) at program startup, then the real
               terminal screen size will be (tried to be) determined once.
               (Normally the sh(1) manages these variables, and unsets them for
               pipe specifications etc.)

     DEAD      The name of the (mailbox) folder to use for saving aborted
               messages if save is set; this defaults to ~/dead.letter.  If the
               variable debug is set no output will be generated, otherwise the
               contents of the file will be replaced.  Except shell globs
               Filename transformations (also see folder) will be performed.

     EDITOR    Pathname of the text editor to use for the edit command and ~e
               (see COMMAND ESCAPES); VISUAL is used for a more display oriented
               editor.

     HOME      The user's home directory.  This variable is only used when it
               resides in the process environment.  The calling user's home
               directory will be used instead if this directory does not exist,
               is not accessible or cannot be read; it will always be used for
               the root user.  (No test for being writable is performed to allow
               usage by non-privileged users within read-only jails, but
               dependent on settings this directory is a default write target
               for, for example, DEAD, MBOX and more.)

     LC_ALL, LC_CTYPE, LANG
               [Option] The (names in lookup order of the) locale(7) (and / or
               see setlocale(3)) which indicates the used Character sets.
               Runtime changes trigger automatic updates of the entire locale
               system, which includes updating ttycharset (except during startup
               if the variable has been frozen via -S).

     LINES     The user's preferred number of lines for the terminal screen.
               The behaviour is as described for COLUMNS, yet the compile-time
               constant used in non-interactive mode and as a fallback defaults
               to 24 (lines).

     LISTER    Pathname of the directory lister to use in the folders command
               when operating on local mailboxes.  Default is ls(1) (path search
               through SHELL).

     LOGNAME   Upon startup Mail will actively ensure that this variable refers
               to the name of the user who runs Mail, in order to be able to
               pass a verified name to any newly created child process.

     MAIL      Is used as the user's primary system mailbox unless inbox is set.
               If the environmental fallback is also not set, a built-in
               compile-time default is used.  This is assumed to be an absolute
               pathname.

     MAILCAPS  [Option] Override the default path search of The Mailcap files:
               any existing file therein will be loaded in sequence, appending
               any content to the list of MIME type handler directives.  The RFC
               1524 standard imposed default value is assigned otherwise:
               ‘~/.mailcap:/etc/mailcap:/usr/etc/mailcap:
               /usr/local/etc/mailcap’.  (The default value is a compile-time
               [Option].)

     MAILRC    Is used as a startup file instead of ~/.mailrc if set.  In order
               to avoid side-effects from configuration files scripts should
               either set this variable to /dev/null or the -: command line
               option should be used.

     MAILX_NO_SYSTEM_RC
               If this variable is set then reading of mail.rc (aka
               system-mailrc) at startup is inhibited, i.e., the same effect is
               achieved as if Mail had been started up with the option -: (and
               according argument) or -n.  This variable is only used when it
               resides in the process environment.

     MBOX      The name of the user's secondary mailbox file.  A logical subset
               of the special Filename transformations (also see folder) are
               supported.  The default is ~/mbox.  Traditionally this MBOX is
               used as the file to save messages from the primary system mailbox
               that have been read.  Also see Message states.

     NETRC     [v15-compat][Option] This variable overrides the default location
               of the user's ~/.netrc file.

     PAGER     Pathname of the program to use for backing the command more, and
               when the crt variable enforces usage of a pager for output.  The
               default paginator is more(1) (path search through SHELL).

               Mail inspects the contents of this variable: if its contains the
               string “less” then a non-existing environment variable LESS will
               be set to ‘Ri’, likewise for “lv” LV will optionally be set to
               ‘-c’.  Also see colour-pager.

     PATH      A colon-separated list of directories that is searched by the
               shell when looking for commands, for example
               ‘/bin:/usr/bin:/usr/local/bin’.

     POSIXLY_CORRECT
               This environment entry is automatically squared with posix.

     SHELL     The shell to use for the commands !, shell, the ~! COMMAND
               ESCAPES and when starting subprocesses.  A default shell is used
               if this environment variable is not defined.

     SOCKS5_PROXY
               This environment entry is automatically squared with socks-proxy.

     SOURCE_DATE_EPOCH
               Specifies a time in seconds since the Unix epoch (1970-01-01) to
               be used in place of the current time.  This variable is looked up
               upon program startup, and its existence will switch Mail to a
               reproducible mode (https://reproducible-builds.org) which uses
               deterministic random numbers, a special fixated pseudo LOGNAME
               and more.  This operation mode is used for development and by
               software packagers.  [v15 behaviour may differ] Currently an
               invalid setting is only ignored, rather than causing a program
               abortion.

                     $ SOURCE_DATE_EPOCH=`date +%s` mail

     TERM      [Option] The terminal type for which output is to be prepared.
               For extended colour and font control please refer to Coloured
               display, and for terminal management in general to On terminal
               control and line editor.

     TMPDIR    Except for the root user this variable defines the directory for
               temporary files to be used instead of /tmp (or the given compile-
               time constant) if set, existent, accessible as well as read- and
               writable.  This variable is only used when it resides in the
               process environment, but Mail will ensure at startup that this
               environment variable is updated to contain a usable temporary
               directory.

     USER      Identical to LOGNAME (see there), but this variable is not
               standardized, should therefore not be used, and is only corrected
               if already set.

     VISUAL    Pathname of the text editor to use for the visual command and ~v
               (see COMMAND ESCAPES); EDITOR is used for a less display oriented
               editor.

FILES
     ~/.mailcap, /etc/mailcap
               [Option] Personal and system-wide MIME type handler definition
               files, see The Mailcap files.  (The shown names are part of the
               RFC 1524 standard search path MAILCAPS.)

     ~/.mailrc, mail.rc
               User-specific and system-wide files giving initial commands, the
               Resource files.  (The used filenames come from MAILRC and
               system-mailrc, respectively.)

     ~/mbox    The default value for MBOX.

     ~/.mime.types, /etc/mime.types
               Personal and system-wide MIME types, see The mime.types files.

     ~/.netrc  [v15-compat][Option] The default location of the user's .netrc
               file – the section The .netrc file documents the file format.
               The used path can be set via NETRC.

     /dev/null
               The data sink null(4).

     ~/.rnd    [Option] Possible location for persistent random entropy seed
               storage, see tls-rand-file.

   Resource files
     Upon startup Mail reads in several resource files, in order:

     mail.rc   System wide initialization file (system-mailrc).  Reading of this
               file can be suppressed, either by using the -: (and according
               argument) or -n command line options, or by setting the
               ENVIRONMENT variable MAILX_NO_SYSTEM_RC.

     ~/.mailrc
               File giving initial commands.  A different file can be chosen by
               setting the ENVIRONMENT variable MAILRC.  Reading of this file
               can be suppressed with the -: command line option.

     mailx-extra-rc
               Defines a startup file to be read after all other resource files.
               It can be used to specify settings that are not understood by
               other mailx(1) implementations, for example.

     The content of these files is interpreted as follows:

     The whitespace characters space, tabulator and newline, as well as
         those defined by the variable ifs, are removed from the beginning and
         end of input lines.
     Empty lines are ignored.
     Any other line is interpreted as a command.  It may be spread over
         multiple input lines if the newline character is “escaped” by placing a
         reverse solidus character ‘\’ as the last character of the line;
         whereas any leading whitespace of follow lines is ignored, trailing
         whitespace before a escaped newline remains in the input.
     If the line (content) starts with the number sign ‘#’ then it is a
         comment-command and also ignored.  (The comment-command is a real
         command, which does nothing, and therefore the usual follow lines
         mechanism applies!)

     Errors while loading these files are subject to the settings of errexit and
     posix.  More files with syntactically equal content can be sourceed.  The
     following, saved in a file, would be an examplary content:

            # This line is a comment command.  And y\
               es, it is really continued here.
           set debug \
               verbose
               set editheaders

   The mime.types files
     As stated in HTML mail and MIME attachments Mail needs to learn about MIME
     (Multipurpose Internet Mail Extensions) media types in order to classify
     message and attachment content.  One source for them are mime.types files,
     the loading of which can be controlled by setting the variable
     mimetypes-load-control.  Another is the command mimetype, which also offers
     access to Mails MIME type cache.  mime.types files have the following
     syntax:

           type/subtype extension [extension ...]
           # For example text/html html htm

     where ‘type/subtype’ define the MIME media type, as standardized in RFC
     2046: ‘type’ is used to declare the general type of data, while the
     ‘subtype’ specifies a specific format for that type of data.  One or
     multiple filename ‘extension’s, separated by whitespace, can be bound to
     the media type format.  Comments may be introduced anywhere on a line with
     a number sign ‘#’, causing the remaining line to be discarded.  Mail also
     supports an extended, non-portable syntax in especially crafted files,
     which can be loaded via the alternative value syntax of
     mimetypes-load-control, and prepends an optional ‘type-marker’:

           [type-marker ]type/subtype extension [extension ...]

     The following type markers are supported:

     ?         Treat message parts with this content as plain text.
     ?t        The same as plain ?.
     ?h        Treat message parts with this content as HTML tagsoup.  If the
               [Option]al HTML-tagsoup-to-text converter is not available treat
               the content as plain text instead.
     ?H        Likewise ?h, but instead of falling back to plain text require an
               explicit content handler to be defined.
     ?q        If no handler can be found a text message is displayed which says
               so.  This can be annoying, for example signatures serve a
               contextual purpose, their content is of no use by itself.  This
               marker will avoid displaying the text message.

     Further reading: for sending messages: mimetype, mime-allow-text-controls,
     mimetypes-load-control.  For reading etc. messages: HTML mail and MIME
     attachments, The Mailcap files, mimetype, mime-counter-evidence,
     mimetypes-load-control, pipe-TYPE/SUBTYPE, pipe-EXTENSION.

   The Mailcap files
     [Option] RFC 1524 defines a “User Agent Configuration Mechanism” to be used
     to inform mail user agent programs about the locally installed facilities
     for handling various data formats, i.e., about commands and how they can be
     used to display, edit et cetera MIME part contents, as well as a default
     path search that includes multiple possible locations of resource files,
     and the MAILCAPS environment variable to overwrite that.  Handlers found
     from doing the path search will be cached, the command mailcap operates on
     that cache, and the variable mailcap-disable will suppress automatic
     loading, and usage of any mailcap handlers.  HTML mail and MIME attachments
     gives a general overview of how MIME types are handled.

     “Mailcap” files consist of a set of newline separated entries.  Comment
     lines start with a number sign ‘#’ (in the first column!) and are ignored.
     Empty lines are ignored.  All other lines are interpreted as mailcap
     entries.  An entry definition may be split over multiple lines by placing
     the reverse solidus character ‘\’ last in all but the final line.  The
     standard does not specify how leading whitespace of successive lines is to
     be treated, therefore they are retained.

     “Mailcap” entries consist of a number of semicolon ‘;’ separated fields.
     The first two fields are mandatory and must occur in the specified order,
     the remaining fields are optional and may appear in any order.  Leading and
     trailing whitespace of field content is ignored (removed).  The reverse
     solidus ‘\’ character can be used to escape any following character
     including semicolon and itself in the content of the second field, and in
     value parts of any optional key/value field.

     The first field defines the MIME ‘TYPE/SUBTYPE’ the entry is about to
     handle (case-insensitively).  If the subtype is specified as an asterisk
     ‘*’ the entry is meant to match all subtypes of the named type, e.g.,
     ‘audio/*’ would match any audio type.  The second field is the view shell
     command used to display MIME parts of the given type.

     Data consuming shell commands will be fed message (MIME part) data on
     standard input unless one or more instances of the (unquoted) string ‘%s’
     are used: these formats will be replaced with a temporary file(name) that
     has been prefilled with the parts data.  Data producing shell commands are
     expected to generata data on their standard output unless that format is
     used.  In all cases any given ‘%s’ format is replaced with a properly shell
     quoted filename.  When a command requests a temporary file via ‘%s’ then
     that will be removed again, as if the x-mailx-tmpfile and
     x-mailx-tmpfile-fill flags had been set; unless the command requests
     x-mailx-async the x-mailx-tmpfile-unlink flag is also implied; see below
     for more.

     Optional fields define single-word flags (case-insensitive), or key / value
     pairs consisting of a case-insensitive keyword, an equals sign ‘=’, and a
     shell command; whitespace surrounding the equals sign is removed.  Optional
     fields include the following:

     compose   A program that can be used to compose a new body or body part in
               the given format.  (Currently unused.)

     composetyped
               Similar to the compose field, but is to be used when the
               composing program needs to specify the ‘Content-type:’ header
               field to be applied to the composed data.  (Currently unused.)

     copiousoutput
               A flag field which indicates that the output of the view command
               is integrable into Mails normal visual display.  It is mutually
               exclusive with needsterminal.

     description
               A textual description that describes this type of data.  The text
               may optionally be enclosed within double quotation marks ‘"’.

     edit      A program that can be used to edit a body or body part in the
               given format.  (Currently unused.)

     nametemplate
               This field specifies a filename format for the ‘%s’ format used
               in the shell command fields, in which ‘%s’ will be replaced by a
               random string.  (The filename is also stored in and passed to
               subprocesses via MAILX_FILENAME_TEMPORARY.)  The standard says
               this is “only expected to be relevant in environments where
               filename extensions are meaningful”, and so this field is ignored
               unless the ‘%s’ is a prefix, optionally followed by (ASCII)
               alphabetic and numeric characters, the underscore and the period.
               For example, to specify that a JPG file is to be passed to an
               image viewer with a name ending in ‘.jpg’, ‘nametemplate=%s.jpg’
               can be used.

     needsterminal
               This flag field indicates that the given shell command must be
               run on an interactive terminal.  Mail will temporarily release
               the terminal to the given command in interactive mode, in non-
               interactive mode this entry will be entirely ignored; this flag
               implies x-mailx-noquote.

     print     A program that can be used to print a message or body part in the
               given format.  (Currently unused.)

     test      Specifies a program to be run to test some condition, for
               example, the machine architecture, or the window system in use,
               to determine whether or not this mailcap entry applies.  If the
               test fails, a subsequent mailcap entry should be sought; also see
               x-mailx-test-once.  Standard I/O of the test program is
               redirected from and to /dev/null, and the format ‘%s’ is not
               supported (the data does not yet exist).

     textualnewlines
               A flag field which indicates that this type of data is line-
               oriented and that, if encoded in ‘base64’, all newlines should be
               converted to canonical form (CRLF) before encoding, and will be
               in that form after decoding.  (Currently unused.)

     x11-bitmap
               Names a file, in X11 bitmap (xbm) format, which points to an
               appropriate icon to be used to visually denote the presence of
               this kind of data.  This field is not used by Mail.

     x-mailx-async
               Extension flag field that denotes that the given view command
               shall be executed asynchronously, without blocking Mail.  Cannot
               be used in conjunction with needsterminal; the standard output of
               the command will go to /dev/null.

     x-mailx-noquote
               An extension flag field that indicates that even a copiousoutput
               view command shall not be used when quoteing messages, as it
               would by default.

     x-mailx-test-once
               Extension flag which denotes whether the given test command shall
               be evaluated once only with its exit status being cached.  This
               is handy if some global unchanging condition is to be queried,
               like “running under the X Window System”.

     x-mailx-tmpfile
               Extension flag field that requests creation of a zero-sized
               temporary file, the name of which is to be placed in the
               environment variable MAILX_FILENAME_TEMPORARY.  It is an error to
               use this flag with commands that include a ‘%s’ format (because
               that is implemented by means of this temporary file).

     x-mailx-tmpfile-fill
               Normally the MIME part content is passed to the handler via
               standard input; if this flag is set then the data will instead be
               written into the implied x-mailx-tmpfile.  In order to cause
               deletion of the temporary file you will have to set
               x-mailx-tmpfile-unlink explicitly!  It is an error to use this
               flag with commands that include a ‘%s’ format.

     x-mailx-tmpfile-unlink
               Extension flag field that requests that the temporary file shall
               be deleted automatically when the command loop is entered again
               at latest.  It is an error to use this flag with commands that
               include a ‘%s’ format, or in conjunction with x-mailx-async.
               x-mailx-tmpfile is implied.

     The standard includes the possibility to define any number of additional
     fields, prefixed by ‘x-’.  Flag fields apply to the entire “Mailcap” entry
     — in some unusual cases, this may not be desirable, but differentiation can
     be accomplished via separate entries, taking advantage of the fact that
     subsequent entries are searched if an earlier one does not provide enough
     information.  For example, if a view command needs to specify the
     needsterminal flag, but the compose command shall not, the following will
     help out the latter:

           application/postscript; ps-to-terminal %s; needsterminal
           application/postscript; ps-to-terminal %s; compose=idraw %s

     In value parts of command fields any occurrence of the format string ‘%t’
     will be replaced by the ‘TYPE/SUBTYPE’ specification.  Any named parameter
     from a messages' ‘Content-type:’ field may be embedded into the command
     line using the format ‘%{’ followed by the parameter name and a closing
     brace ‘}’ character.  The entire parameter should appear as a single
     command line argument, regardless of embedded spaces, shell quoting will be
     performed by the RFC 1524 processor, thus:

           # Message
           Content-type:  multipart/mixed; boundary=42

           # Mailcap file
           multipart/*; /usr/local/bin/showmulti \
             %t %{boundary}  ;  composetyped  = /usr/local/bin/makemulti

           # Executed shell command
           /usr/local/bin/showmulti multipart/mixed 42

     Note that Mail does not support handlers for multipart MIME parts as shown
     in this example (as of today).  It does not support the additional formats
     ‘%n’ and ‘%F’.  An example file, also showing how to properly deal with the
     expansion of ‘%s’, which includes any quotes that are necessary to make it
     a valid shell argument by itself and thus will cause undesired behaviour
     when placed in additional user-provided quotes:

           # Comment line
           text/richtext; richtext %s; copiousoutput

           text/x-perl; perl -cWT %s; nametemplate = %s.pl

           # Exit EX_TEMPFAIL=75 on signal
           application/pdf; \
             infile=%s\; \
               trap "rm -f ${infile}" EXIT\; \
               trap "exit 75" INT QUIT TERM\; \
               mupdf "${infile}"; \
             test = [ -n "${DISPLAY}" ]; \
             nametemplate = %s.pdf; x-mailx-async
           application/pdf; pdftotext -layout - -; copiousoutput

           application/*; echo "This is \\"%t\\" but \
               is 50 \% Greek to me" \; < %s head -c 512 | cat -vet; \
             copiousoutput; x-mailx-noquote

     Further reading: HTML mail and MIME attachments, The mime.types files,
     mimetype, MAILCAPS, mime-counter-evidence, pipe-TYPE/SUBTYPE,
     pipe-EXTENSION.

   The .netrc file
     User credentials for machine accounts (see On URL syntax and credential
     lookup) can be placed in the .netrc file, which will be loaded and cached
     when requested by netrc-lookup.  The default location ~/.netrc may be
     overridden by the NETRC environment variable.  As long as syntax
     constraints are honoured the file source may be replaced with the output of
     the shell command set in netrc-pipe, to load an encrypted file, for
     example.  The cache can be managed with the command netrc.

     The file consists of space, tabulator or newline separated tokens.  This
     parser implements a superset of the original BSD syntax, but users should
     nonetheless be aware of portability glitches, shall their .netrc be usable
     across multiple programs and platforms:

     BSD only supports double quotation marks, for example ‘password "pass
         with spaces"’.
     BSD (only?) supports escaping of single characters via a reverse
         solidus (a space could be escaped via ‘\ ’), in- as well as outside of
         a quoted string.  This method is assumed to be present, and will
         actively be used to quote double quotation marks ‘"’ and reverse
         solidus ‘\’ characters inside the login and password tokens, for
         example for display purposes.
     BSD does not require a final quotation mark of the last user input
         token.
     The original BSD (Berknet) parser also supported a format which allowed
         tokens to be separated with commas – whereas at least Hewlett-Packard
         still seems to support this syntax, this parser does not!
     As a non-portable extension some widely-used programs support shell-
         style comments: if an input line starts, after any amount of
         whitespace, with a number sign ‘#’, then the rest of the line is
         ignored.
     Whereas other programs may require that the .netrc file is accessible
         by only the user if it contains a password token for any other login
         than “anonymous”, this parser will always require these strict
         permissions.

     Of the following list of supported tokens this parser uses (and caches)
     machine, login and password.  An existing default entry will not be used.

     machine name
               The hostname of the entries' machine, lowercase-normalized before
               use.  Any further file content, until either end-of-file or the
               occurrence of another machine or a default first-class token is
               bound (only related) to the machine name.

               As an extension that should not be the cause of any worries this
               parser supports a single wildcard prefix for name:

                     machine *.example.com login USER password PASS
                     machine pop3.example.com login USER password PASS
                     machine smtp.example.com login USER password PASS

               which would match ‘xy.example.com’ as well as ‘pop3.example.com’,
               but neither ‘example.com’ nor ‘local.smtp.example.com’.  In the
               example neither ‘pop3.example.com’ nor ‘smtp.example.com’ will be
               matched by the wildcard, since the exact matches take precedence
               (it is however faster to specify it the other way around).

     default   This is the same as machine except that it is a fallback entry
               that is used shall none of the specified machines match; only one
               default token may be specified, and it must be the last first-
               class token.

     login name
               The user name on the remote machine.

     password string
               The user's password on the remote machine.

     account string
               Supply an additional account password.  This is merely for FTP
               purposes.

     macdef name
               Define a macro.  A macro is defined with the specified name; it
               is formed from all lines beginning with the next line and
               continuing until a blank line is (consecutive newline characters
               are) encountered.  (Note that macdef entries cannot be utilized
               by multiple machines, too, but must be defined following the
               machine they are intended to be used with.)  If a macro named
               init exists, it is automatically run as the last step of the
               login process.  This is merely for FTP purposes.

EXAMPLES
   An example configuration
           # This example assumes v15.0 compatibility mode
           set v15-compat

           # Request strict TLL transport layer security checks
           set tls-verify=strict

           # Where are the up-to-date TLS certificates?
           # (Since we manage up-to-date ones explicitly, do not use any,
           # possibly outdated, default certificates shipped with OpenSSL)
           #set tls-ca-dir=/etc/ssl/certs
           set tls-ca-file=/etc/ssl/certs/ca-certificates.crt
           set tls-ca-no-defaults
           #set tls-ca-flags=partial-chain
           wysh set smime-ca-file="${tls-ca-file}" \
             smime-ca-no-defaults #smime-ca-flags="${tls-ca-flags}"

           # This could be outsourced to a central configuration file via
           # tls-config-file plus tls-config-module if the used library allows.
           # CipherString: explicitly define the list of ciphers, which may
           #   improve security, especially with protocols older than TLS v1.2.
           #   See ciphers(1).  Possibly best to only use tls-config-pairs-HOST
           #   (or -USER@HOST), as necessary, again..
           #   Note that TLSv1.3 uses Ciphersuites= instead, which will join
           #   with CipherString (if protocols older than v1.3 are allowed)
           # Curves: especially with TLSv1.3 curves selection may be desired.
           # MinProtocol,MaxProtocol: do not use protocols older than TLS v1.2.
           #   Change this only when the remote server does not support it:
           #   maybe use chain support via tls-config-pairs-HOST / -USER@HOST
           #   to define such explicit exceptions, then, e.g.,
           #     MinProtocol=TLSv1.1
           if [ "$tls-features" =% +ctx-set-maxmin-proto ]
             wysh set tls-config-pairs='\
                 CipherString=TLSv1.2:!aNULL:!eNULL:@STRENGTH,\
                 Curves=P-521:P-384:P-256,\
                 MinProtocol=TLSv1.1'
           else
             wysh set tls-config-pairs='\
                 CipherString=TLSv1.2:!aNULL:!eNULL:@STRENGTH,\
                 Curves=P-521:P-384:P-256,\
                 Protocol=-ALL\,+TLSv1.1 \, +TLSv1.2\, +TLSv1.3'
           endif

           # Essential setting: select allowed character sets
           set sendcharsets=utf-8,iso-8859-1

           # A very kind option: when replying to a message, first try to
           # use the same encoding that the original poster used herself!
           set reply-in-same-charset

           # When replying, do not merge From: and To: of the original message
           # into To:.  Instead old From: -> new To:, old To: -> merge Cc:.
           set recipients-in-cc

           # When sending messages, wait until the Mail-Transfer-Agent finishs.
           # Only like this you will be able to see errors reported through the
           # exit status of the MTA (including the built-in SMTP one)!
           set sendwait

           # Only use built-in MIME types, no mime.types(5) files
           set mimetypes-load-control

           # Default directory where we act in (relative to $HOME)
           set folder=mail
           # A leading "+" (often) means: under *folder*
           # *record* is used to save copies of sent messages
           set MBOX=+mbox.mbox DEAD=+dead.txt \
             record=+sent.mbox record-files record-resent

           # Make "file mymbox" and "file myrec" go to..
           shortcut mymbox %:+mbox.mbox myrec +sent.mbox

           # Not really optional, e.g., for S/MIME
           set from='Your Name <address@exam.ple>'

           # It may be necessary to set hostname and/or smtp-hostname
           # if the "SERVER" of mta and "domain" of from do not match.
           # The `urlencode' command can be used to encode USER and PASS
           set mta=(smtps?|submissions?)://[USER[:PASS]@]SERVER[:PORT] \
             smtp-auth=login/plain... \
             smtp-use-starttls

           # Never refuse to start into interactive mode, and more
           set emptystart \
             colour-pager crt= \
             followup-to followup-to-honour=ask-yes fullnames \
             history-file=+.mailhist history-size=-1 history-gabby \
             mime-counter-evidence=0b1111 \
             prompt='?\$?!\$!/\$^ERRNAME[\$account#\$mailbox-display]? ' \
             reply-to-honour=ask-yes \
             umask=

           # Only include the selected header fields when typing messages
           headerpick type retain from_ date from to cc subject \
             message-id mail-followup-to reply-to
           # ...when forwarding messages
           headerpick forward retain subject date from to cc
           # ...when saving message, etc.
           #headerpick save ignore ^Original-.*$ ^X-.*$

           # Some mailing lists
           mlist '@xyz-editor\.xyz$' '@xyzf\.xyz$'
           mlsubscribe '^xfans@xfans\.xyz$'

           # Handle a few file extensions (to store MBOX databases)
           filetype bz2 'bzip2 -dc' 'bzip2 -zc' \
             gz 'gzip -dc' 'gzip -c'  xz 'xz -dc' 'xz -zc' \
             zst 'zstd -dc' 'zstd -19 -zc' \
             zst.pgp 'gpg -d | zstd -dc' 'zstd -19 -zc | gpg -e'

           # A real life example of a very huge free mail provider
           # Instead of directly placing content inside `account',
           # we `define' a macro: like that we can switch "accounts"
           # from within *on-compose-splice*, for example!
           define XooglX {
             set folder=~/spool/XooglX inbox=+syste.mbox sent=+sent
             set from='Your Name <address@examp.ple>'

             set pop3-no-apop-pop.gmXil.com
             shortcut pop %:pop3s://pop.gmXil.com
             shortcut imap %:imaps://imap.gmXil.com
             # Or, entirely IMAP based setup
             #set folder=imaps://imap.gmail.com record="+[Gmail]/Sent Mail" \
             #   imap-cache=~/spool/cache

             set mta=smtp://USER:PASS@smtp.gmXil.com smtp-use-starttls
             # Alternatively:
             set mta=smtps://USER:PASS@smtp.gmail.com:465
           }
           account XooglX {
             \call XooglX
           }

           # Here is a pretty large one which does not allow sending mails
           # if there is a domain name mismatch on the SMTP protocol level,
           # which would bite us if the value of from does not match, e.g.,
           # for people who have a sXXXXeforge project and want to speak
           # with the mailing list under their project account (in from),
           # still sending the message through their normal mail provider
           define XandeX {
             set folder=~/spool/XandeX inbox=+syste.mbox sent=+sent
             set from='Your Name <address@exam.ple>'

             shortcut pop %:pop3s://pop.yaXXex.com
             shortcut imap %:imaps://imap.yaXXex.com

             set mta=smtps://USER:PASS@smtp.yaXXex.com:465 \
               hostname=yaXXex.com smtp-hostname=
           }
           account XandeX {
             \call Xandex
           }

           # Create some new commands so that, e.g., `ls /tmp' will..
           commandalias lls '!ls ${LS_COLOUR_FLAG} -aFlrS'
           commandalias llS '!ls ${LS_COLOUR_FLAG} -aFlS'

           set pipe-message/external-body='?* echo $MAILX_EXTERNAL_BODY_URL'

           # We do not support gpg(1) directly yet.  But simple --clearsign'd
           # message parts can be dealt with as follows:
           define V {
             localopts yes
             wysh set pipe-text/plain=$'?*#++=?\
               < "${MAILX_FILENAME_TEMPORARY}" awk \
                   -v TMPFILE="${MAILX_FILENAME_TEMPORARY}" \'\
                 BEGIN{done=0}\
                 /^-----BEGIN PGP SIGNED MESSAGE-----/,/^$/ {\
                   if(done++ != 0)\
                     next;\
                   print "--- GPG --verify ---";\
                   system("gpg --verify " TMPFILE " 2>&1");\
                   print "--- GPG --verify ---";\
                   print "";\
                   next;\
                 }\
                 /^-----BEGIN PGP SIGNATURE-----/,\
                     /^-----END PGP SIGNATURE-----/{\
                   next;\
                 }\
                 {print}\
               \''
               print
           }
           commandalias V '\'call V

     When storing passwords in ~/.mailrc appropriate permissions should be set
     on this file with ‘$ chmod 0600 ~/.mailrc’.  If the [Option]al netrc-lookup
     is available user credentials can be stored in the central ~/.netrc file
     instead; e.g., here is a different version of the example account that sets
     up SMTP and POP3:

           define XandeX {
             set folder=~/spool/XandeX inbox=+syste.mbox sent=+sent
             set from='Your Name <address@exam.ple>'
             set netrc-lookup
             # Load an encrypted ~/.netrc by uncommenting the next line
             #set netrc-pipe='gpg -qd ~/.netrc.pgp'

             set mta=smtps://smtp.yXXXXx.ru:465 \
                 smtp-hostname= hostname=yXXXXx.com
             set pop3-keepalive=240 pop3-no-apop-pop.yXXXXx.ru
             commandalias xp fi pop3s://pop.yXXXXx.ru
           }
           account XandeX {
             \call XandeX
           }

     and, in the ~/.netrc file:

           machine *.yXXXXx.ru login USER password PASS

     This configuration should now work just fine:

           $ echo text | mail -dvv -AXandeX -s Subject user@exam.ple

   S/MIME step by step
     [Option] The first thing that is needed for Signed and encrypted messages
     with S/MIME is a personal certificate, and a private key.  The certificate
     contains public information, in particular a name and email address(es),
     and the public key that can be used by others to encrypt messages for the
     certificate holder (the owner of the private key), and to verify signed
     messages generated with that certificate('s private key).  Whereas the
     certificate is included in each signed message, the private key must be
     kept secret.  It is used to decrypt messages that were previously encrypted
     with the public key, and to sign messages.

     For personal use it is recommended to get a S/MIME certificate from one of
     the major CAs on the Internet.  Many CAs offer such certificates for free.
     Usually offered is a combined certificate and private key in PKCS#12 format
     which Mail does not accept directly.  To convert it to PEM format, the
     following shell command can be used; please read on for how to use these
     PEM files.

           $ openssl pkcs12 -in cert.p12 -out certpem.pem -clcerts -nodes
           $ # Alternatively
           $ openssl pkcs12 -in cert.p12 -out cert.pem -clcerts -nokeys
           $ openssl pkcs12 -in cert.p12 -out key.pem -nocerts -nodes

     There is also https://www.CAcert.org which issues client and server
     certificates to members of their community for free; their root certificate
     (https://www.cacert.org/certs/root.crt) is often not in the default set of
     trusted CA root certificates, though, which means their root certificate
     has to be downloaded separately, and needs to be part of the S/MIME
     certificate validation chain by including it in smime-ca-dir or as a vivid
     member of the smime-ca-file.  But let us take a step-by-step tour on how to
     setup S/MIME with a certificate from CAcert.org despite this situation!

     First of all you will have to become a member of the CAcert.org community,
     simply by registrating yourself via the web interface.  Once you are,
     create and verify all email addresses you want to be able to create signed
     and encrypted messages for/with using the corresponding entries of the web
     interface.  Now ready to create S/MIME certificates, so let us create a new
     “client certificate”, ensure to include all email addresses that should be
     covered by the certificate in the following web form, and also to use your
     name as the “common name”.

     Create a private key and a certificate request on your local computer
     (please see the manual pages of the used commands for more in-depth
     knowledge on what the used arguments etc. do):

           $ openssl req -nodes -newkey rsa:4096 -keyout key.pem -out creq.pem

     Afterwards copy-and-paste the content of “creq.pem” into the certificate-
     request (CSR) field of the web form on the CAcert.org website (you may need
     to unfold some “advanced options” to see the corresponding text field).
     This last step will ensure that your private key (which never left your
     box) and the certificate belong together (through the public key that will
     find its way into the certificate via the certificate-request).  You are
     now ready and can create your CAcert certified certificate.  Download and
     store or copy-and-paste it as “pub.crt”.

     Yay.  In order to use your new S/MIME setup a combined private key/public
     key (certificate) file has to be created:

           $ cat key.pem pub.crt > ME@HERE.com.paired

     This is the file Mail will work with.  If you have created your private key
     with a passphrase then Mail will ask you for it whenever a message is
     signed or decrypted, unless this operation has been automated as described
     in Signed and encrypted messages with S/MIME.  Set the following variables
     to henceforth use S/MIME (setting smime-ca-file is of interest for
     verification only):

           ? set smime-ca-file=ALL-TRUSTED-ROOT-CERTS-HERE \
               smime-sign-cert=ME@HERE.com.paired \
               smime-sign-digest=SHA512 \
               smime-sign from=myname@my.host

   Using CRLs with S/MIME or TLS
     [Option] Certification authorities (CAs) issue certificate revocation lists
     (CRLs) on a regular basis.  These lists contain the serial numbers of
     certificates that have been declared invalid after they have been issued.
     Such usually happens because the private key for the certificate has been
     compromised, because the owner of the certificate has left the organization
     that is mentioned in the certificate, etc.  To seriously use S/MIME or TLS
     verification, an up-to-date CRL is required for each trusted CA.  There is
     otherwise no method to distinguish between valid and invalidated
     certificates.  Mail currently offers no mechanism to fetch CRLs, nor to
     access them on the Internet, so they have to be retrieved by some external
     mechanism.

     Mail accepts CRLs in PEM format only; CRLs in DER format must be converted,
     like, e.g.:

           $ openssl crl -inform DER -in crl.der -out crl.pem

     To tell Mail about the CRLs, a directory that contains all CRL files (and
     no other files) must be created.  The smime-crl-dir or tls-crl-dir
     variables, respectively, must then be set to point to that directory.
     After that, Mail requires a CRL to be present for each CA that is used to
     verify a certificate.

FAQ
     In general it is a good idea to turn on debug (-d) and / or verbose (-v,
     twice) if something does not work well.  Very often a diagnostic message
     can be produced that leads to the problems' solution.

   Mail shortly hangs on startup
     This can have two reasons, one is the necessity to wait for a file lock and
     cannot be helped, the other being that Mail calls the function uname(2) in
     order to query the nodename of the box (sometimes the real one is needed
     instead of the one represented by the internal variable hostname).  One may
     have varying success by ensuring that the real hostname and ‘localhost’
     have entries in /etc/hosts, or, more generally, that the name service is
     properly setup – and does hostname(1) return the expected value?  Does this
     local hostname have a domain suffix?  RFC 6762 standardized the link-local
     top-level domain ‘.local’, try again after adding an (additional) entry
     with this extension.

   I cannot login to Google mail (via OAuth)
     Since 2014 some free service providers classify programs as “less secure”
     unless they use a special authentication method (OAuth 2.0) which was not
     standardized for non-HTTP protocol authentication token query until August
     2015 (RFC 7628).

     Different to Kerberos / GSSAPI, which is developed since the mid of the
     1980s, where a user can easily create a local authentication ticket for
     her- and himself with the locally installed kinit(1) program, that protocol
     has no such local part but instead requires a world-wide-web query to
     create or fetch a token; since there is no local cache this query would
     have to be performed whenever Mail is invoked (in interactive sessions
     situation may differ).

     Mail does not directly support OAuth.  It, however, supports XOAUTH2 /
     OAUTHBEARER, see But, how about XOAUTH2 / OAUTHBEARER? If that is not used
     it is necessary to declare Mail a “less secure app” (on the providers
     account web page) in order to read and send mail.  However, it also seems
     possible to take the following steps instead:

     1.   give the provider the number of a mobile phone,
     2.   enable “2-Step Verification”,
     3.   create an application specific password (16 characters), and
     4.   use that special password instead of the real Google account password
          in Mail (for more on that see the section On URL syntax and credential
          lookup).

   But, how about XOAUTH2 / OAUTHBEARER?
     Following up I cannot login to Google mail (via OAuth) one OAuth-based
     authentication method is available: the OAuth 2.0 bearer token usage as
     standardized in RFC 6750 (according SASL mechanism in RFC 7628), also known
     as XOAUTH2 and OAUTHBEARER, allows fetching a temporary access token via
     the web that can locally be used as a password.  The protocol is simple and
     extendable, token updates or even password changes via a simple TLS secured
     server login would be possible in theory, but today a web browser and an
     external support tool are prerequisites for using this authentication
     method.  The token times out and must be periodically refreshed via the
     web.

     Some hurdles must be taken before being able to use this method.  Using
     GMail as an example, an application (that is a name) must be registered,
     for which credentials, a “client ID” and a “client secret”, need to be
     created and saved locally (in a secure way).  These initial configuration
     steps can be performed at
     https://console.developers.google.com/apis/credentials Thereafter a refresh
     token can be requested; a python program to do this for GMail accounts is
     https://github.com/google/gmail-oauth2-tools/raw/master/python/oauth2.py:

           $ python oauth2.py --user=EMAIL \
             --client-id=THE-ID --client-secret=THE-SECRET \
             --generate_oauth2_token
           To authorize token, visit this url and follow the directions:
             https://accounts.google.com/o/oauth2/auth?client_id=...
             Enter verification code: ...
             Refresh Token: ...
             Access Token: ...
             Access Token Expiration Seconds: 3600
           $ # Of which the last three are actual token responses.
           $ # Thereafter access tokens can regulary be refreshed
           $ # via the created refresh token (read on)

     The generated refresh token must also be saved locally (securely).  The
     procedure as a whole can be read at https://github.com/google/gmail-
     oauth2-tools/wiki/OAuth2DotPyRunThrough Since periodic timers are not yet
     supported, keeping an access token up-to-date (from within Mail) can only
     be performed via the hook on-main-loop-tick, or (for sending only)
     on-compose-enter (for more on authentication please see the section On URL
     syntax and credential lookup):

           set on-main-loop-tick=o-m-l-t on-compose-enter=o-c-e
           define o-m-l-t {
             xcall update_access_token
           }
           define o-c-e {
             xcall update_access_token
           }

           set access_token_=0
           define update_access_token {
             local set i epoch_sec epoch_nsec
             vput vexpr i epoch
             eval set $i # set epoch_sec/_nsec of vexpr epoch
             vput vexpr i + $access_token_ 2100
             if $epoch_sec -ge $i
               vput ! password python oauth2.py --user=EMAIL \
                   --client-id=THE-ID --client-secret=THE-SECRET \
                   --refresh-token=THE-REFRESH-TOKEN |\
                 sed '1b PASS;d; :PASS s/^.\{1,\}:\(.\{1,\}\)$/\1/'
               vput csop password trim "$password"
               if -n "$verbose"
                 echo password is <$password>
               endif
               set access_token_=$epoch_sec
             endif
           }

   Not "defunctional", but the editor key does not work
     Two thinkable situations: the first is a shadowed sequence; setting debug,
     or the most possible verbose mode, causes a printout of the bind tree after
     that is built; being a cache, this happens only upon startup or after
     modifying bindings.

     Or second, terminal libraries (see On terminal control and line editor,
     bind, termcap) may report different codes than the terminal really sends,
     rendering bindings dysfunctional because expected and received data do not
     match; the verbose listing of bindings will show the byte sequences that
     are expected.  (One common source of problems is that the — possibly even
     non-existing — keypad is not turned on, and the resulting layout reports
     the keypad control codes for the normal keyboard keys.)

     To overcome the situation use for example the program cat(1) with its
     option -v, if available, to see the byte sequences which are actually
     produced by keypresses, and use the variable termcap to make Mail aware of
     them.  The terminal this is typed on produces some unexpected sequences,
     here for an example the shifted home key:

           ? set verbose
           ? bind*
           # 1B 5B=[ 31=1 3B=; 32=2 48=H
             bind base :kHOM z0
           ? x
           $ cat -v
           ^[[H
           $ mail -v -Stermcap='kHOM=\E[H'
           ? bind*
           # 1B 5B=[ 48=H
             bind base :kHOM z0

   Can Mail git-send-email?
     Yes.  Put (at least parts of) the following in your ~/.gitconfig:

           [sendemail]
           smtpserver = /usr/bin/mail
           smtpserveroption = -t
           #smtpserveroption = -Sexpandaddr
           smtpserveroption = -Athe-account-you-need
           ##
           suppresscc = all
           suppressfrom = false
           assume8bitEncoding = UTF-8
           #to = /tmp/OUT
           confirm = always
           chainreplyto = true
           multiedit = false
           thread = true
           quiet = true
           annotate = true

     Patches can also be send directly, for example:

           $ git mail-patch HEAD^ |
             mail -Athe-account-you-need -t RECEIVER

   Howto handle stale dotlock files
     folder sometimes fails to open MBOX mail databases because creation of
     dotlock files is impossible due to existing but unowned lock files.  Mail
     does not offer an option to deal with those files, because it is considered
     a site policy what counts as unowned, and what not.  The site policy is
     usually defined by administrator(s), and expressed in the configuration of
     a locally installed MTA (for example Postfix ‘stale_lock_time=500s’).
     Therefore the suggestion:

           $ </dev/null mail -s 'MTA: be no frog, handle lock' $LOGNAME

     By sending a mail to yourself the local MTA can use its normal queue
     mechanism to try the delivery multiple times, finally decide a lock file
     has become stale, and remove it.

IMAP CLIENT
     [Option]ally there is IMAP client support available.  This part of the
     program is obsolete and will vanish in v15 with the large MIME and I/O
     layer rewrite, because it uses old-style blocking I/O and makes excessive
     use of signal based long code jumps.  Support can hopefully be readded
     later based on a new-style I/O, with SysV signal handling.  In fact the
     IMAP support had already been removed from the codebase, but was
     reinstantiated on user demand: in effect the IMAP code is at the level of
     Mail v14.8.16 (with imapcodec being the sole exception), and should be
     treated with some care.

     IMAP uses the ‘imap://’ and ‘imaps://’ protocol prefixes, and an IMAP-based
     folder may be used.  IMAP URLs (paths) undergo inspections and possible
     transformations before use (and the command imapcodec can be used to
     manually apply them to any given argument).  Hierarchy delimiters are
     normalized, a step which is configurable via the imap-delim variable chain,
     but defaults to the first seen delimiter otherwise.  Mail supports
     internationalised IMAP names, and en- and decodes the names from and to the
     ttycharset as necessary and possible.  If a mailbox name is expanded (see
     Filename transformations) to an IMAP mailbox, all names that begin with `+'
     then refer to IMAP mailboxes below the folder target box, while folder
     names prefixed by `@' refer to folders below the hierarchy base, so the
     following will list all folders below the current one when in an IMAP
     mailbox: ‘folders @’.

     Note: some IMAP servers do not accept the creation of mailboxes in the
     hierarchy base, but require that they are created as subfolders of `INBOX'
     – with such servers a folder name of the form

           imaps://mylogin@imap.myisp.example/INBOX.

     should be used (the last character is the server's hierarchy delimiter).
     The following IMAP-specific commands exist:

     cache     Only applicable to cached IMAP mailboxes; takes a message list
               and reads the specified messages into the IMAP cache.

     connect   If operating in disconnected mode on an IMAP mailbox, switch to
               online mode and connect to the mail server while retaining the
               mailbox status.  See the description of the disconnected variable
               for more information.

     disconnect
               If operating in online mode on an IMAP mailbox, switch to
               disconnected mode while retaining the mailbox status.  See the
               description of the disconnected variable for more.  A list of
               messages may optionally be given as argument; the respective
               messages are then read into the cache before the connection is
               closed, thus ‘disco *’ makes the entire mailbox available for
               disconnected use.

     imap      Sends command strings directly to the current IMAP server.  Mail
               operates always in IMAP `selected state' on the current mailbox;
               commands that change this will produce undesirable results and
               should be avoided.  Useful IMAP commands are:

                     create         Takes the name of an IMAP mailbox as an
                                    argument and creates it.

                     getquotaroot   (RFC 2087) Takes the name of an IMAP mailbox
                                    as an argument and prints the quotas that
                                    apply to the mailbox.  Not all IMAP servers
                                    support this command.

                     namespace      (RFC 2342) Takes no arguments and prints the
                                    Personal Namespaces, the Other User's
                                    Namespaces and the Shared Namespaces.  Each
                                    namespace type is printed in parentheses; if
                                    there are multiple namespaces of the same
                                    type, inner parentheses separate them.  For
                                    each namespace a prefix and a hierarchy
                                    separator is listed.  Not all IMAP servers
                                    support this command.

     imapcodec
               Perform IMAP path transformations.  Supports vput (see Command
               modifiers), and manages the error number !.  The first argument
               specifies the operation: e[ncode] normalizes hierarchy delimiters
               (see imap-delim) and converts the strings from the locale
               ttycharset to the internationalized variant used by IMAP,
               d[ecode] performs the reverse operation.  Encoding will honour
               the (global) value of imap-delim.

     The following IMAP-specific internal variables exist:

     disconnected
               (Boolean) When an IMAP mailbox is selected and this variable is
               set, no connection to the server is initiated.  Instead, data is
               obtained from the local cache (see imap-cache).  Mailboxes that
               are not present in the cache and messages that have not yet
               entirely been fetched from the server are not available; to fetch
               all messages in a mailbox at once, the command `copy * /dev/null'
               can be used while still in connected mode.  Changes that are made
               to IMAP mailboxes in disconnected mode are queued and committed
               later when a connection to that server is made.  This procedure
               is not completely reliable since it cannot be guaranteed that the
               IMAP unique identifiers (UIDs) on the server still match the ones
               in the cache at that time.  Data is saved to DEAD when this
               problem occurs.

     disconnected-USER@HOST
               The specified account is handled as described for the
               disconnected variable above, but other accounts are not affected.

     imap-auth-USER@HOST, imap-auth
               Sets the IMAP authentication method.  Supported are the default
               ‘login’, [v15-compat] ‘oauthbearer’ (see FAQ entry But, how about
               XOAUTH2 / OAUTHBEARER?), [v15-compat] ‘external’ and ‘externanon’
               (for TLS secured connections which pass a client certificate via
               tls-config-pairs), as well as the [Option]al ‘cram-md5’ and
               ‘gssapi’.  All methods need a user and a password except ‘gssapi’
               and ‘external’, which only need the former.  ‘externanon’ solely
               builds upon the credentials passed via a client certificate, and
               is usually the way to go since tested servers do not actually
               follow RFC 4422, and fail if additional credentials are actually
               passed.

     imap-cache
               Enables caching of IMAP mailboxes.  The value of this variable
               must point to a directory that is either existent or can be
               created by Mail.  All contents of the cache can be deleted by
               Mail at any time; it is not safe to make assumptions about them.

     imap-delim-USER@HOST, imap-delim-HOST, imap-delim
               The hierarchy separator used by the IMAP server.  Whenever an
               IMAP path is specified it will undergo normalization.  One of the
               normalization steps is the squeezing and adjustment of hierarchy
               separators.  If this variable is set, any occurrence of any
               character of the given value that exists in the path will be
               replaced by the first member of the value; an empty value will
               cause the default to be used, it is ‘/.’.  If not set, we will
               reuse the first hierarchy separator character that is discovered
               in a user-given mailbox name.

     imap-keepalive-USER@HOST, imap-keepalive-HOST, imap-keepalive
               IMAP servers may close the connection after a period of
               inactivity; the standard requires this to be at least 30 minutes,
               but practical experience may vary.  Setting this variable to a
               numeric `value' greater than 0 causes a `NOOP' command to be sent
               each `value' seconds if no other operation is performed.

     imap-list-depth
               When retrieving the list of folders on an IMAP server, the
               folders command stops after it has reached a certain depth to
               avoid possible infinite loops.  The value of this variable sets
               the maximum depth allowed.  The default is 2.  If the folder
               separator on the current IMAP server is a slash `/', this
               variable has no effect and the folders command does not descend
               to subfolders.

     imap-use-starttls-USER@HOST, imap-use-starttls-HOST, imap-use-starttls
               Causes Mail to issue a `STARTTLS' command to make an unencrypted
               IMAP session TLS encrypted.  This functionality is not supported
               by all servers, and is not used if the session is already
               encrypted by the IMAPS method.

SEE ALSO
     bogofilter(1), gpg(1), more(1), newaliases(1), openssl(1), sendmail(1),
     sh(1), spamassassin(1), iconv(3), setlocale(3), aliases(5), termcap(5),
     terminfo(5), locale(7), mailaddr(7), re_format(7) (or regex(7)),
     mailwrapper(8), sendmail(8)

HISTORY
     M. Douglas McIlroy writes in his article “A Research UNIX Reader: Annotated
     Excerpts from the Programmer's Manual, 1971-1986” that a mail(1) command
     already appeared in First Edition UNIX in 1971:

           Electronic mail was there from the start.  Never satisfied with its
           exact behavior, everybody touched it at one time or another: to
           assure the safety of simultaneous access, to improve privacy, to
           survive crashes, to exploit uucp, to screen out foreign freeloaders,
           or whatever.  Not until v7 did the interface change (Thompson).
           Later, as mail became global in its reach, Dave Presotto took charge
           and brought order to communications with a grab-bag of external
           networks (v8).

     BSD Mail, in large parts compatible with UNIX mail, was written in 1978 by
     Kurt Shoens and developed as part of the BSD UNIX distribution until 1995.
     This manual page is derived from “The Mail Reference Manual” that Kurt
     Shoens wrote for Mail 1.3, included in 3BSD in 1980.  The common UNIX and
     BSD denominator became standardized as mailx(1) in the X/Open Portability
     Guide Issue 2 (January 1987).  After the rise of Open Source BSD variants
     Mail saw continuous development in the individual code forks, noticeably by
     Christos Zoulas in NetBSD.  Based upon this Nail, later Heirloom Mailx, was
     developed by Gunnar Ritter in the years 2000 until 2008.  Since 2012 S-nail
     is maintained by Steffen Nurpmeso.

     Electronic mail exchange in general is a concept even older.  The earliest
     well documented electronic mail system was part of the Compatible Time
     Sharing System (CTSS) at MIT, its MAIL command had been proposed in a staff
     planning memo at the end of 1964 and was implemented in mid-1965 when Tom
     Van Vleck and Noel Morris wrote the necessary code.  Similar communication
     programs were built for other timesharing systems.  One of the most
     ambitious and influential was Murray Turoff's EMISARI.  Created in 1971 for
     the United States Office of Emergency Preparedness, EMISARI combined
     private electronic messages with a chat system, public postings, voting,
     and a user directory.

     During the 1960s it was common to connect a large number of terminals to a
     single, central computer.  Connecting two computers together was relatively
     unusual.  This began to change with the development of the ARPANET, the
     ancestor of today's Internet.  In 1971 Ray Tomlinson adapted the SNDMSG
     program, originally developed for the University of California at Berkeley
     timesharing system, to give it the ability to transmit a message across the
     network into the mailbox of a user on a different computer.  For the first
     time it was necessary to specify the recipient's computer as well as an
     account name.  Tomlinson decided that the underused commercial at ‘@’ would
     work to separate the two.

     Sending a message across the network was originally treated as a special
     instance of transmitting a file, and so a MAIL command was included in RFC
     385 on file transfer in 1972.  Because it was not always clear when or
     where a message had come from, RFC 561 in 1973 aimed to formalize
     electronic mail headers, including “from”, “date”, and “subject”.  In 1975
     RFC 680 described fields to help with the transmission of messages to
     multiple users, including “to”, “cc”, and “bcc”.  In 1977 these features
     and others went from best practices to a binding standard in RFC 733.
     Queen Elizabeth II of England became the first head of state to send
     electronic mail on March 26 1976 while ceremonially opening a building in
     the British Royal Signals and Radar Establishment (RSRE) in Malvern.

AUTHORS
     Kurt Shoens, Edward Wang, Keith Bostic, Christos Zoulas, Gunnar Ritter.
     Mail is developed by Steffen Nurpmeso <s-mailx@lists.sdaoden.eu>.

CAVEATS
     [v15 behaviour may differ] Interrupting an operation via SIGINT aka
     ‘control-C’ from anywhere else but a command prompt is very problematic and
     likely to leave the program in an undefined state: many library functions
     cannot deal with the siglongjmp(3) that this software (still) performs;
     even though efforts have been taken to address this, no sooner but in v15
     it will have been worked out: interruptions have not been disabled in order
     to allow forceful breakage of hanging network connections, for example (all
     this is unrelated to ignore).

     The SMTP and POP3 protocol support of Mail is very basic.  Also, if it
     fails to contact its upstream SMTP server, it will not make further
     attempts to transfer the message at a later time (setting save and sendwait
     may be useful).  If this is a concern, it might be better to set up a local
     SMTP server that is capable of message queuing.

BUGS
     When a network-based mailbox is open, directly changing to another network-
     based mailbox of a different protocol (i.e., from POP3 to IMAP or vice
     versa) will cause a “deadlock”.

     After deleting some message of a POP3 mailbox the header summary falsely
     claims that there are no messages to display, one needs to perform a scroll
     or dot movement to restore proper state.

     In ‘thread’ed sort mode a power user may encounter crashes very
     occasionally (this is may and very).

     Please report bugs to the contact-mail address, for example from within
     mail: ‘? eval mail $contact-mail’.  Including the verbose output of the
     command version may be helpful:

           ? wysh set escape=! verbose; vput version xy; unset verbose;\
             eval mail $contact-mail
           Bug subject
           !I xy
           !.

     Information on the web at ‘$ mail -X 'echo $contact-web; x'’.

BSD                              April 26, 2020                              BSD