mail

MAIL(1)                     General Commands Manual                    MAIL(1)

NAME
     Mail [v14.9.15] — 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.  Using -d
           or -v enables obsoletion warnings.

           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 the
            spec then the system wide mail.rc is sourced, likewise the letter
            ‘u’ controls sourcing of the user's personal ~/.mailrc file,
            whereas the letters ‘-’ and ‘/’ explicitly forbid sourcing of any
            resource files.  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 ~^).  Filename transformations (also see file) will be
            performed, except that shell variables are not expanded.  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
            supported without support for character set conversions (features
            does not mention ‘+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, e.g., ‘-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
            Almost enable a sandbox mode with the internal variable debug; the
            same can be achieved via ‘-S debug’ or ‘set debug’.

     -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 file).  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 file (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, --header-search=..
            Display a summary of headers of all messages that match the given
            spec in the file 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 (e.g., by using the option -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 file opened will be in read-only mode.

     -r from-addr, --from-address=..
            Whereas the source address that appears in the from header of a
            message (or in the sender header if the former contains multiple
            addresses) is honoured by the built-in SMTP transport, it is not
            used by a file-based mta (Mail-Transfer-Agent) for the RFC 5321
            reverse-path used for relaying and delegating a message to its
            destination(s), for delivery errors etc., but it 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, e.g., ‘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
            setting the internal variable verbose enables display of some
            informational context messages.  (Will increase the level of
            verbosity when used multiple times.)

     -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 be used to, e.g., 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'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 purposes.  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.

     Because Mail strives for compliance with POSIX mailx(1) it is likely that
     some configuration settings have to be adjusted before using it is a
     smooth experience.  (Rather complete configuration examples can be found
     in the section EXAMPLES.)  The provided global mail.rc (one of the
     Resource files) template bends those standard imposed settings of the
     INTERNAL VARIABLES a bit towards more user friendliness and safety,
     however.

     For example, it sets hold and keepsave 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 if posix aka POSIXLY_CORRECT mode
     has been enabled) to avoid mangling of file permissions when files
     eventually get recreated.

     To enter interactive mode even if the initial mailbox is empty it sets
     emptystart, 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.

     Some 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.

   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 -:/ -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 -. \
               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; e.g., ~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
     file 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, e.g., user names can be expanded
     to network addresses by specifying ‘namehostex’.  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 \
                 -. 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 file 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,
     e.g., to use file names with leading vertical bars or commercial ats.
     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 ‘File 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 file) 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), e.g., ‘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, e.g., 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 file) 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).  The command Lreply
     knows 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
     Messages which are HTML-only become more and more common, and of course
     many messages come bundled with a bouquet of MIME (Multipurpose Internet
     Mail Extensions) parts.  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 faulty MIME part declarations which are often seen in
     real-life messages, setting mime-counter-evidence will allow verification
     of the given assertion, and possible provision of an alternative, better
     MIME type.

     Whereas Mail [Option]ally supports a simple HTML-to-text filter for
     displaying HTML messages (indicated by ‘+filter-html-tagsoup’ in
     features), it cannot handle MIME types other than plain text itself.
     Instead programs need to become registered to deal with specific MIME
     types or file extensions.  These programs may either prepare plain text
     versions of their input in order to enable Mail to integrate their output
     neatlessly in its own message visualization (a mode which is called
     copiousoutput), or display the content themselves, for example in an
     external graphical window: such handlers will only be considered by and
     for the command mimeview.

     To install a handler program for a specific MIME type an according
     pipe-TYPE/SUBTYPE variable needs to be set; to instead define a handler
     for a specific file extension the respective pipe-EXTENSION variable can
     be used – these handlers take precedence.  [Option]ally Mail supports
     mail user agent configuration as defined in RFC 1524; this mechanism (see
     The Mailcap files) will be queried for display or quote handlers if none
     of the former two did; it will be the sole source for handlers of other
     purpose.  A last source for handlers is the MIME type definition itself,
     if a type-marker has been registered with the command mimetype, which
     many of the built-in MIME types do.

     For example, to display a HTML message inline (converted to a more fancy
     plain text representation than the built-in filter is capable to produce)
     with either of the text-mode browsers lynx(1) or elinks(1), teach Mail
     about MathML documents and make it display them as plain text, and to
     open PDF attachments in an external PDF viewer, asynchronously and with
     some other magic attached:

           ? if [ "$features" !% +filter-html-tagsoup ]
           ?   #set pipe-text/html='?* elinks -force-html -dump 1'
           ?   set pipe-text/html='?* lynx -stdin -dump -force_html'
           ?   # Display HTML as plain text instead
           ?   #set pipe-text/html=?
           ? endif
           ? mimetype ? application/mathml+xml mathml
           ? wysh set pipe-application/pdf='?&=? \
               trap "rm -f \"${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 and Lreply), 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, e.g., when list-replying via
     Lreply, when 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
     such address which contains 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.

           ? 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.

   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
     becoming 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

     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.  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
     [v15-compat] For accessing protocol-specific resources usage of Uniform
     Resource Locators (URL, RFC 3986) has become omnipresent.  Mail expects
     and understands URLs in a “normalized” variant which is 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 in question, or because the part is protocol-specific, e.g.,
     ‘/path’ is used by the [Option]al Maildir file type and the IMAP
     protocol, but not by POP3.  If as part of the URL any of ‘USER’ and
     ‘PASSWORD’ is specified, then the URL percent encoded form must be used
     (RFC 3986; the command urlcodec can be used to perform the encoding):

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

     Many internal variables of Mail exist in multiple versions, called
     variable chains for the rest of this document: the plain ‘variable’ as
     well as ‘variable-HOST’ and ‘variable-USER@HOST’.  Here ‘HOST’ indeed
     means ‘server:port’ if a ‘port’ had been specified in the respective URL,
     otherwise it refers to the plain ‘server’.  Also, ‘USER’ is not truly the
     ‘USER’ that had been found when doing the user chain lookup as is
     described below, i.e., this ‘USER’ will never be in URL percent encoded
     form, whether it came from an URL or not; i.e., variable chain name
     extensions of INTERNAL VARIABLES must not be URL percent encoded.

     For example, whether an hypothetical URL ‘smtp://hey%3Ayou@our.house’ had
     been given that includes a user, or whether the URL was
     ‘smtp://our.house’ and the user had been found differently, to lookup the
     variable chain smtp-use-starttls Mail first looks for whether ‘smtp-use-
     starttls-hey:you@our.house’ is defined, then whether ‘smtp-use-starttls-
     our.house’ exists before finally ending up looking at the plain variable
     itself.

     Mail obeys the following logic scheme when dealing with the necessary
     credential information of an account:

     ·   A user is always required.  If no ‘USER’ has been given in the URL
         the variables user-HOST and user are looked up.  If no such
         variable(s) can be found then Mail will, when enforced by the
         [Option]al variables netrc-lookup-HOST or netrc-lookup, search The
         .netrc file of the user for a ‘HOST’ specific entry which provides a
         ‘login’ name: this lookup will only succeed if unambiguous (one
         possible matching entry for ‘HOST’).

         If there is still no ‘USER’ then Mail will fall back to the user who
         is supposed to run Mail, the identity of which has been fixated
         during Mail startup and is known to be a valid user on the current
         host.

     ·   Authentication: unless otherwise noted this will lookup the
         PROTOCOL-auth-USER@HOST, PROTOCOL-auth-HOST, PROTOCOL-auth variable
         chain, falling back to a protocol-specific default should this have
         no success.

     ·   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 already
         provided the password, too.  Otherwise the variable chain
         password-USER@HOST, password-HOST, password is looked up and used if
         existent.

         Afterwards the complete [Option]al variable chain
         netrc-lookup-USER@HOST, netrc-lookup-HOST, netrc-lookup is looked up.
         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 that 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.  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

     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 is that of certificates: as part of each network
     connection setup a (set of) certificates will be exchanged, and by using
     those the identity of the network peer can be cryptographically verified;
     if possible the TLS/SNI (ServerNameIndication) extension will be enabled
     in order to allow servers fine-grained control over the certificates
     being used.  TLS works by using a locally installed pool of trusted
     certificates, and verifying the connection peer succeeds if that provides
     a certificate which has been issued or is trusted by any certificate in
     the trusted local pool.

     The local pool of trusted so-called CA (Certification Authority)
     certificates is usually delivered with the used TLS library, and will be
     selected automatically.  It is also possible to use a specific pool of
     trusted certificates.  If this is desired, tls-ca-no-defaults should be
     set to avoid using the default certificate pool, and tls-ca-file and/or
     (with special preparation) tls-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.  For inspection or other
     purposes, the certificate of a server (as seen when connecting to it) can
     be fetched like this:

           $ </dev/null openssl s_client -showcerts -connect \
               the-server.example:pop3s 2>&1 | tee log.txt

     Mail also supports a mode of operation in which certificates are not at
     all matched against a local pool of CA certificates.  Instead a message
     digest will be calculated for the certificate presented by the connection
     peer, and be compared against tls-fingerprint (a variable chain that
     picks up ‘USER@HOST’ or ‘HOST’ context-dependent variable variants), and
     the connection will succeed if the calculated digest equals the expected
     one.  The used message digest can be configured via (the chain)
     tls-fingerprint-digest.  The command tls may be helpful.

     It depends on the used protocol whether encrypted communication is
     possible, and which configuration steps have to be taken to enable it.
     Some protocols, e.g., 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 specify the allowed protocols or cipher
     lists that a communication channel may use.  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) can be used and 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, e.g.,
     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, e.g., 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 (e.g.,
     to add a missing LATIN1 to ISO-8859-1 mapping), or to enforce treatment
     of one character set as another one (e.g., to 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 from aka search, type and delete, can be given a list of message
     numbers as arguments to apply to a number of messages at once.  Thus
     ‘delete 1 2’ deletes 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.  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.

     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, e.g.,

                 '@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 quotes ‘"’ 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, e.g., ‘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 will be realized through one of the standard
     UNIX libraries, either the Termcap Access Library (libtermcap,
     -ltermcap), or, alternatively, the Terminal Information Library
     (libterminfo, -lterminfo), both of which will be initialized to work with
     the environment variable TERM.  Terminal control will enhance or enable
     interactive usage aspects, e.g., Coloured display, and extend behaviour
     of the Mailx-Line-Editor (MLE), which may learn the byte-sequences of
     keys like the cursor- and function-keys.

     The internal variable termcap can be used to overwrite settings or to
     learn (correct(ed)) keycodes.  Actual library interaction can be disabled
     completely by setting termcap-disable; termcap will be queried
     regardless, which is true even if the [Option]al library support has not
     been enabled at configuration time as long as some other [Option] which
     (may) query terminal control sequences has been enabled.  Mail can be
     told to enter an alternative exclusive screen, the so-called ca-mode, by
     setting termcap-ca-mode; this requires sufficient terminal support, and
     the used PAGER may also need special configuration, dependent on the
     value of crt.

     [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 the internal variable 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 fine 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, e.g.,
     ‘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; combinations not mentioned either cause job control
     signals or do not generate a (unique) keycode:

     ‘\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] Mail can be configured to support a coloured display and font
     attributes by emitting ANSI aka ISO 6429 SGR (select graphic rendition)
     escape sequences.  Usage of colours and font attributes solely depends
     upon the capability of the detected terminal type that is defined by the
     environment variable TERM and which can be fine-tuned by the user via the
     internal variable termcap.

     On top of what Mail knows about the terminal the boolean variable
     colour-pager defines whether the actually applicable colour and font
     attribute sequences should also be generated when output is going to be
     paged through the external program defined by the environment variable
     PAGER (also see crt).  This is not enabled by default because different
     pager programs need different command line switches or other
     configuration in order to support those sequences.  Mail however knows
     about some widely used pagers and in a clean environment it is often
     enough to simply set colour-pager; please refer to that variable for more
     on this topic.

     Colours and font attributes can be managed with the multiplexer command
     colour, and uncolour can be used to remove mappings of a given colour
     type.  If the variable colour-disable is set then any active usage of
     colour and font attribute sequences is suppressed without affecting
     possibly established colour mappings.  Since colours are available if any
     of the standard I/O descriptors it opened on a terminal, it might make
     sense to conditionalize the colour setup by encapsulating it with 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.

     The command list can be used to show the list of all commands, either
     alphabetically sorted or in prefix search order (these do not match, also
     because the POSIX standard prescribes a set of abbreviations).
     [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 one or 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, e.g., ‘\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, e.g., 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 old, traditional
     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, e.g., 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, e.g., 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, e.g.,
                       ‘^G’, the reverse solidus notation has been
                       standardized: ‘\cG’.  Some control codes also have
                       standardized (ISO-10646, ISO C) aliases, as shown above
                       (e.g., ‘\a’, ‘\n’, ‘\t’): 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, e.g., 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, e.g.,

           ? 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.

           ·   The filename is matched against the following patterns or
               strings:

               #      (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.
               %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, e.g., the command file:
                      the file will be treated as a primary system mailbox by,
                      e.g., 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, e.g., 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, e.g.,
           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, e.g., 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, e.g., ‘?h’, ‘?hel’ and ‘?help’ and see how the
           output changes.  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 file), 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 the Postfix MTA aliases(5) rules, and may consist of
           alphabetic characters, digits, the underscore, the number sign,
           colon, commercial at and hyphen-minus; extensions: exclamation mark
           ‘!’, period ‘.’ as well as “any character that has the high bit
           set” may be used: ‘[[:alnum:]_#:@!.-]+’.  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, e.g., ‘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 binding is (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, and any
           remaining arguments form the expansion.  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.

           “Keys” which form the binding are specified as a comma-separated
           list of byte-sequences, where each list entry corresponds to one
           key(press).  A list entry may, indicated by a leading colon
           character ‘:’, also refer to the name of a terminal capability;
           several dozen names will be 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.  It is possible to use any capability, 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, so that an exact match is required to update or remove
           a binding.  Examples:

                 ? 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, before being
           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.

           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.

           It is advisable to use an initial escape or other control character
           (e.g., ‘\cA’) for bindings which describe user key combinations (as
           opposed to purely terminal capability based ones), in order to
           avoid ambiguities whether input belongs to key sequences or not; it
           also reduces search time.  Adjusting bind-timeout may help shall
           keys and sequences be falsely recognized.

     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    (ch) Change the working directory to HOME or the given argument.
           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, e.g., 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
           (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.  The type of colour is given as the (case-
           insensitive) first argument, which 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.  Monochrome terminals cannot deal with
           colours, but only (some) font attributes.

           Without further arguments the list of all currently defined
           mappings for the given colour type is shown (as a special case
           giving ‘all’ or ‘*’ will show the mappings of all types).
           Otherwise the second argument defines the mappable slot, and the
           third argument a (comma-separated list of) colour and font
           attribute specification(s), and the optional 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
           precondition available depend on the mappable slot (see Coloured
           display for some examples), 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) Copy messages to files whose names are derived from the author
           of the respective message and do not mark them as being saved;
           otherwise identical to Save.

     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, e.g.,
           ‘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, e.g., 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
                 }

                 # E.g.
                 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 read or readall commands.

           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 Status
                 ? digmsg $msgno header show Status;readall x;echon $x
                 212 Status
                 RO

                 ? 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 except that is echoes to
           standard error.  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] Mail has a strict notion about which
           variables are INTERNAL VARIABLES and which are managed in the
           program ENVIRONMENT.  Since some of the latter are a vivid part of
           Mails functioning, however, they are transparently integrated into
           the normal handling of internal variables via set and unset.  To
           integrate other environment variables of choice into this
           transparent handling, and also to export internal variables into
           the process environment where they normally are not, a ‘link’ needs
           to become established with this command, as in, e.g.,

                 environ link PERL5LIB TZ

           Afterwards changing such variables with set will cause automatic
           updates of the program environment, and therefore be inherited by
           newly created child processes.  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
           program environment, but in any way the knowledge they ever have
           been ‘link’ed will be lost.  Note that this implies that localopts
           may cause loss of such links.

           The command ‘unlink’ will remove an existing link, but leaves the
           variables as such intact.  Additionally the subcommands ‘set’ and
           ‘unset’ are provided, which work exactly the same as the documented
           commands set and unset, but (additionally un)link the variable(s)
           with the program environment and thus immediately export them to,
           or remove them from (if possible), respectively, the program
           environment.

     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 file, but open the mailbox read-only.

     file  (fi) The file command switches to a new mailbox.  Without arguments
           it shows status information of the current mailbox.  If an argument
           is given, it will write out changes (such as deletions) the user
           has made, open a new mailbox, update the internal variables
           mailbox-resolved and mailbox-display, execute an according
           folder-hook, if one is installed, and optionally display a summary
           of headers if the variable header is set.

           Filename transformations will be applied to the name argument, and
           ‘protocol://’ prefixes are, i.e., URL syntax is understood, e.g.,
           ‘mbox:///tmp/mdirbox’: if a protocol prefix is used the mailbox
           type is fixated and neither the auto-detection (read on) nor the
           newfolders mechanisms apply.  [Option]ally URLs can also be used to
           access network resources, which may be accessed securely via
           Encrypted network communication if so supported.  Network
           communication socket timeouts are configurable, e.g.,
           socket-connect-timeout.  All generated network traffic may be
           proxied over the SOCKS5 server given in 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.

           If the resulting file protocol (MBOX database) name is located on a
           local filesystem then the list of all registered filetypes is
           traversed in order to see whether a transparent intermediate
           conversion step is necessary to handle the given mailbox, in which
           case Mail will use the found hook to load and save data into and
           from a temporary file, respectively.  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'

           filetypes also provide limited (case-sensitive) auto-completion
           capabilities.  For example ‘mbox.gz’ will be found for ‘? file
           mbox’ provided that a corresponding handler is installed.  It will
           neither find ‘mbox.GZ’ nor ‘mbox.Gz’ however, on the other hand
           doing an explicit ‘? file mbox.GZ’ will find and use the handler
           for ‘gz’.

           MBOX databases will always be protected via file-region locks
           (fcntl(2)) during file operations in order to avoid inconsistencies
           due to concurrent modifications.  [Option] In addition mailbox
           files treated as the system inbox (MAIL), as well as primary system
           mailboxes in general 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 for the duration of the
           synchronization — as necessary an external privileged dotlock
           helper will be used to create the dotlock file in the same
           directory and with the same user and group identities as the file
           of interest.  dotlock-disable can be used to turn off additional
           dotlock files, shall the need arise.  There is also a related entry
           in the FAQ: Howto handle stale dotlock files.

           Mail by default uses tolerant POSIX rules when reading MBOX
           database files, but it will detect invalid message boundaries in
           this mode and complain (even more with debug) if any is seen: in
           this case mbox-rfc4155 can be used to create a valid MBOX database
           from the invalid input.

           [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.

           [v15 behaviour may differ] If no protocol has been fixated and no
           existing file has been found, the variable newfolders controls the
           format of mailboxes yet to be created.

     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 file.  The extensions
           are used case-insensitively, yet the auto-completion feature of,
           e.g., file 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) The same as file.

     folders
           With no arguments, list the names of the folders in the folder
           directory.  With an existing folder as an argument, lists the names
           of folders below the named folder.

     Followup
           (F) Similar to Respond, but saves the message in a file named after
           the local part of the first recipient's address (instead of in
           record).

     followup
           (fo) Similar to respond, but saves the message in a file named
           after the local part of the first recipient's address (instead of
           in record).

     followupall
           Similar to followup, but responds to all recipients regardless of
           the flipr variable.

     followupsender
           Similar to Followup, but responds to the sender only regardless of
           the flipr variable.

     Forward
           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
           Takes a message and the address of a recipient and forwards the
           message to him.  The text of the original message is included in
           the new one, with the value of the forward-inject-head variable
           preceding, and the value of forward-inject-tail succeeding it.  To
           filter the included header fields to the desired subset use the
           ‘forward’ slot of the white- and blacklisting command headerpick.
           Only the first part of a multipart message is included unless
           forward-as-attachment, and recipient addresses will be stripped
           from comments, names etc. unless the internal variable fullnames is
           set.

           This may generate the errors ^ERR-DESTADDRREQ if no receiver has
           been specified, ^ERR-PERM if some addressees where rejected by
           expandaddr, ^ERR-NODATA if no applicable messages have been given,
           ^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.

     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 (via, e.g., 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, e.g.,
           ‘-1’ will select the last command, the history top.  Please see On
           terminal control and line editor for more on this topic.

     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, e.g., ‘-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,
           e.g., ‘==?’, ‘==?satu’ and ‘==?saturated’ are 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, e.g., ‘==?’ 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, alphabetically sorted.
           If given any non-whitespace argument the list will be shown in the
           order in which command prefixes are searched.  [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 file.
           ‘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, e.g., 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,
                                        e.g., 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
                 }

     Lreply
           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 reply 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-NODATA if no applicable messages have been given,
           ^ERR-IO if an I/O error occurs, ^ERR-NOTSUP if a necessary
           character set conversion fails, and ^ERR-INVAL for other errors.
           Occurrence of some of the errors depend on the value of expandaddr.
           Any error stops processing of further messages.

     Mail  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  (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-NODATA if no applicable messages have been given,
           ^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.  Occurrence of
           some of the errors depend on the value of expandaddr.

     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 one to display MIME parts which require external
           MIME handler programs to run which do not integrate in Mails 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 moves the messages to a file named after the
           local part of the sender address of the first message (instead of
           in record).

     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.

     netrc
           [Option] When used without arguments or if show has been given the
           content of the ~/.netrc cache is shown, loading it first as
           necessary.  If the argument is load then the cache will only be
           initialized and clear will remove its contents.  Note that Mail
           will try to load the file only once, use ‘netrc clear’ to unlock
           further attempts.  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.:><><>

     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 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.  E.g. (this example requires a modern
           shell):

                 $ LC_ALL=C printf 'echon "hey, "\nread a\nyou\necho $a' |\
                   LC_ALL=C 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
           Removes the named files or directories.  Filename transformations
           including shell pathname wildcard pattern expansions (glob(7)) are
           performed on the arguments.  If a name refer to a mailbox, e.g., a
           Maildir mailbox, then a mailbox type specific removal will be
           performed, deleting the complete mailbox.  The user is asked for
           confirmation in interactive mode.

     rename
           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
           (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
           (r) Take a message and group-responds to it by addressing the
           sender and all recipients, subject to alternates processing.
           followup-to, followup-to-honour, reply-to-honour as well as
           recipients-in-cc influence response behaviour.  Unless the internal
           variable fullnames is set recipient addresses will be stripped from
           comments, names etc.  quote as well as quote-as-attachment
           configure whether responded-to message shall be quoted etc.;
           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, ^ERR-PERM if some addressees where rejected by
           expandaddr, ^ERR-NODATA if no applicable messages have been given,
           ^ERR-IO if an I/O error occurs, ^ERR-NOTSUP if a necessary
           character set conversion fails, and ^ERR-INVAL for other errors.
           Occurrence of some of the errors depend on the value of expandaddr.
           Any error stops processing of further messages.

     replyall
           Similar to reply, but initiates a group-reply regardless of the
           value of flipr.

     replysender
           Similar to Reply, but responds to the sender only regardless of the
           value of flipr.

     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, fully expanded addressee.  ‘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.

           This may generate the errors ^ERR-DESTADDRREQ if no receiver has
           been specified, ^ERR-PERM if the addressee was rejected by
           expandaddr, ^ERR-NODATA if no applicable messages have been given,
           ^ERR-IO if an I/O error occurs, ^ERR-NOTSUP if a necessary
           character set conversion fails, and ^ERR-INVAL for other errors.
           Occurrence of some of the errors depend on the value of expandaddr.
           Any error stops processing of further messages.

     Respond
           Same as Reply.

     respond
           Same as reply.

     respondall
           Same as replyall.

     respondsender
           Same as replysender.

     retain
           (ret) Superseded by the multiplexer headerpick.

     return
           Only available inside the scope of a defined macro or an account,
           this will stop evaluation of any further macro content, and return
           execution control to the caller.  The two optional parameters must
           be specified as positive decimal numbers and default to the value
           0: the first argument specifies the signed 32-bit return value
           (stored in ? [v15 behaviour may differ] and later extended to
           signed 64-bit), the second the signed 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 (in
           record and) taking a filename argument; the variable 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.
           Filename transformations will be applied.  To filter the saved
           header fields to the desired subset use the ‘save’ slot of the
           white- and blacklisting command headerpick.

     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, e.g., via 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 file.  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 interruptable.  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, e.g., ‘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.  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.  Note this
           command of course honours the overall TLS configuration.

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

           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.
                     Only available if the term ‘+sockets’ is included in
                     features.

     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,
           e.g., ‘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), e.g., ‘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, e.g.,
           ‘+?’, ‘+?satu’, and ‘+?saturated’ are 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.

           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, in order to echo some stat fields such that
                     ‘vput vexpr v file-stat FILE; eval wysh set $v’ creates
                     accessible variables.

           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, e.g., ‘regex?’ and ‘regex?case’ are 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,
                     e.g., 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 convience 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.

           [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
     Command escapes are available in compose mode, and are used to perform
     special functions when composing messages.  Command escapes are only
     recognized at the beginning of lines, and consist of a trigger (escape),
     and a command character.  The actual escape character can be set via the
     internal variable escape, it defaults to the tilde ‘~’.  Otherwise
     ignored whitespace characters following the escape character will prevent
     a possible addition of the command line to the [Option]al history.

     Unless otherwise noted all compose mode command escapes ensure proper
     updates of the variables which represent the error number ! and the exit
     status ?.  If the variable errexit is set they will, unless stated
     otherwise, error out message compose mode and cause a program exit if an
     operation fails; an effect equivalent to the command modifier ignerr can
     however be achieved by placing a hyphen-minus ‘-’ after (possible
     whitespace following) the escape character.  If the [Option]al key
     bindings are available it is possible to create bindings specifically for
     the compose mode.

     ~~ 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
           Execute the given Mail command.  Not all commands, however, are
           allowed.

     ~< 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 ~^ instead if this is a
           concern).  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.  E.g., 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, e.g., ‘~|| 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.
           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.  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 fields, first the
                  plain network address, e.g., ‘bob@exam.ple’, separated by a
                  single ASCII SP space from the full address as known, e.g.,
                  ‘(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
                  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 (false command usage).  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 of
                              keyword and value tuples, the keyword being
                              separated from the rest of the line with an
                              ASCII SP space character.

                    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 assign the
                              attribute given as the fourth argument, which is
                              expected to be a value tuple of keyword and
                              other data, separated by a ASCII SP space or TAB
                              tabulator character.  If the value part is
                              empty, 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, and
                    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
                              argument (the remains of the line).  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:’ or ‘Bcc:’ support the
                              ‘?single’ modifier to enforce treatment as a
                              single addressee, e.g., ‘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 (e.g., alias, alternates,
                          recipients-in-cc etc.) took place.
                    ‘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.

           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.  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 ‘type’
           white- and blacklist selection of headerpick.  For MIME multipart
           messages, only the first displayable part is included.

     ~H    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.

     ~h    Edit the message header fields ‘To:’, ‘Cc:’, ‘Bcc:’ and ‘Subject:’
           by typing each one in turn and allowing the user to edit the field.

     ~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”.

     ~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.  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) according to the algorithm
           of quote.

     ~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 the usual Filename transformations,
           into the message; if (the expanded) filename is the hyphen-minus
           ‘-’ then standard input is used, e.g., for pasting purposes.  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.

     ~u messages
           Read in the given / current message(s), excluding all headers.

     ~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”, which is a boolean string that can optionally be prefixed
     with the (case-insensitive) term ‘ask-’, as in ‘ask-yes’, which causes
     prompting of the user in interactive mode, with the given boolean as the
     default value.

     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, e.g., ‘2’, ‘3’
           etc.; positional parameters can be shifted off the stack by calling
           shift.  The parameter stack contains, e.g., 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, e.g., 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, e.g., ‘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
           [Option] Terminals generate multi-byte sequences for certain forms
           of input, for example for function and other special keys.  Some
           terminals however do not write these multi-byte sequences as a
           whole, but byte-by-byte, and the latter is what Mail actually
           reads.  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.

     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, e.g., 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,
           e.g., for bug reports, suggestions, or help regarding Mail.  The
           former can be used directly: ‘? eval mail $contact-mail’.

     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) Enables debug messages and obsoletion warnings, disables
           the actual delivery of messages and also implies norecord as well
           as nosave.

     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 ‘namehostex’.  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.  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.  The
           commands replysender, respondsender, followupsender as well as
           replyall, respondall, followupall are not affected by the current
           setting of flipr.

     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
           file 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 file 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, e.g., 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-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.  These variables are ignored if the
           forward-as-attachment variable is set.

     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.  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 enforced to appear
           as the envelope sender address at the MTA protocol level (the RFC
           5321 reverse-path), either by using the -r command line option
           (with an empty argument; see there for the complete picture on this
           topic), or by setting the internal variable 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 (mlist) or mlsubscribed mailing list?
           ‘%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] If a line editor is available then this can be set to name
           the (expandable) path of the location of a permanent history file;
           also see history-size.

     history-gabby
           (Boolean)[Option] Add more entries to the history as is normally
           done.

     history-gabby-persist
           (Boolean)[Option] Mail's own MLE will not save the additional
           history-gabby entries in persistent storage unless this variable is
           set.  On the other hand it will not loose the knowledge of whether
           a persistent entry was gabby or not.  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, e.g., in ‘From:’
           (also see On sending mail, and non-interactive mode, e.g., 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 file 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 (file), possibly
           abbreviated for display purposes.

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

     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
           file, 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.  (E.g., at the time of this writing some
           newsletters ship their full content only in the rich HTML part,
           whereas the plain text part only contains topic subjects.)

     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, e.g., ‘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 (e.g., 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, like, e.g., ISO-8859-1.  The
                   encoding will cause a large overhead for messages in other
                   character sets: e.g., 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 (optionally prefixed with the
           protocol ‘file://’), or [Option]ally a SMTP aka SUBMISSION protocol
           URL, e.g., [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.  [Option]ally Mail can
           take care of expansion of the usual mta-aliases (aliases(5)).

           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 user@exam.ple
                 $ </dev/null mail -:/ -Smta=test://./xy -s ub user@exam.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, e.g., socket-connect-timeout.
           All generated network traffic may be proxied over the SOCKS5 server
           given in socks-proxy.  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 valid path pointing to a text file in MTA
           aliases(5) format, 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 understood, and [v15
           behaviour may differ] ‘:include:/file/name’ directives are not
           supported.  By including ‘-name’ in the setting of expandaddr it
           can be asserted that only expanded names (mail addresses) are
           passed through to the MTA, hard errors occur otherwise.  The file
           content is cached, but variable as well as file size and
           modification time changes will cause an update.

     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.  This variable can be set to
           suppress any such argument.

     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.

     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, e.g., 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) Unless specified as absolute pathnames, causes the
           filename given in the record variable and the sender-based
           filenames for the Copy and Save commands to be interpreted relative
           to the directory given in the folder variable 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, 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 vexpr 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, e.g., 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 1”: 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 $version
                   echo '~^h l'; read hl; vput csop es substring "${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 finishs 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 is 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 whether the
           command relates to history-gabby, 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, e.g., 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, e.g., ‘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, e.g., 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, e.g., ‘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 will be
           set implicitly before the Resource files are loaded if the
           environment variable POSIXLY_CORRECT is set, and adjusting any of
           those two will be reflected by the other one implicitly.  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.
           ·   Upon changing the active file 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 a reply message is started with the quoted original message,
           the lines of which are prefixed by the value of the variable
           indentprefix, taking into account quote-chars and quote-fold.  If
           set to the empty value, the quoted message will be preceded and
           followed by the expansions of the values of quote-inject-head and
           quote-inject-tail, respectively.  None of the headers of the quoted
           message is included in the quote if the value equals ‘noheading’,
           and only the headers selected by the ‘type’ headerpick selection
           are put above the message body for ‘headers’, whereas all headers
           and all MIME parts are included for ‘allheaders’.  Also see
           quote-as-attachment and ~Q, one of the COMMAND ESCAPES.

     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,
           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:’ are by
           default merged into the new ‘To:’.  If this variable is set, only
           the original ‘From:’ ends in the new ‘To:’, the rest is merged into
           ‘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”.

     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.  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,
           e.g., 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.

     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
           private key and include the user's 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.
           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 recipient's 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's addresses using different encryption keys,
           decryption might fail.

           For signing and decryption purposes it is possible to use encrypted
           keys, and the pseudo-host(s) ‘USER@HOST.smime-cert-key’ for the
           private key (and ‘USER@HOST.smime-cert-cert’ for the certificate
           stored in the same file) will be used for performing any necessary
           password lookup, therefore the lookup can be automated via the
           mechanisms described in On URL syntax and credential lookup.  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 needed passwords would then be
           looked up via the pseudo hosts ‘bob@exam.ple.smime-cert-key’ (and
           ‘bob@exam.ple.smime-cert-cert’).  To include intermediate
           certificates, use smime-sign-include-certs.

     smime-sign-digest-USER@HOST, smime-sign-digest
           [Option] Specifies the message digestto 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, e.g., 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 ‘HOST’ from the content of this variable (or, if
           that is the empty string, hostname 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 which (in from) is about to
           send the message.  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 this is set to the hostname (SOCKS URL) of a SOCKS5
           server then Mail will proxy all of its network activities through
           it.  This can be used to proxy SMTP, POP3 etc. network traffic
           through the Tor anonymizer, for example.  The following would
           create a local SOCKS proxy on port 10000 that forwards to the
           machine ‘HOST’, and from which the network traffic is actually
           instantiated:

                 # Create local proxy server in terminal 1 forwarding to HOST
                 $ ssh -D 10000 USER@HOST
                 # Then, start a client that uses it in terminal 2
                 $ mail -Ssocks-proxy-USER@HOST=localhost:10000

     spam-interface
           [Option] In order to use any of the spam-related commands (like,
           e.g., 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)
                     (http://spamassassin.apache.org SpamAssassin) 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, e.g., ‘-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,
           e.g., ‘-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.
           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 terminal
           capabilities, see termcap.  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.  Note the directory search variant requires the
           certificate files to adhere 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, e.g.:

                 # 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
                 # Well that actual program specific configuration section
                 # now can map individual tls-config-module names to sections,
                 # e.g., 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.  Currently supported
           identities are ‘libressl’ (LibreSSL) , ‘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 be calculated with, e.g., ‘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 (e.g., 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), e.g., 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
           (Boolean) This setting, also controllable via the command line
           option -v, causes Mail to be more verbose, e.g., it will display
           obsoletion warnings and TLS certificate chains.  Even though marked
           (Boolean) this option may be set up to three times in order to
           increase the level of verbosity, higher levels show details of the
           actual message delivery, protocol conversations and even variable
           lookups; a single unset verbose is sufficient to disable verbosity
           as such.

     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 that, e.g., 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) file 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.

     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
           the variable settings this directory is a default write target,
           e.g., for 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.
           This is assumed to be an absolute pathname.  If this environmental
           fallback is also not set, a built-in compile-time default is used.

     MAILCAPS
           [Option] Overrides the default path search for The Mailcap files,
           which is defined in the standard RFC 1524 as ‘~/.mailcap:
           /etc/mailcap:/usr/etc/mailcap:/usr/local/etc/mailcap’.  (Mail makes
           it a configuration option, however.)  Note this is not a search
           path, but a path search.

     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 file) 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’.
           Alse see colour-pager.

     PATH  A colon-separated list of directories that is searched by the shell
           when looking for commands, e.g., ‘/bin:/usr/bin:/usr/local/bin’.

     POSIXLY_CORRECT
           This variable is automatically looked for upon startup, see posix
           for more.

     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.

     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
     ~/.mailrc
           User-specific file giving initial commands, one of the Resource
           files.  The actual value is read from MAILRC.

     mail.rc
           System wide initialization file, one of the Resource files.  The
           actual value is read from system-mailrc.

     ~/.mailcap
           [Option] Personal MIME type handler definition file, see The
           Mailcap files.  This location is part of the RFC 1524 standard
           search path, which is a configuration option and can be overridden
           via MAILCAPS.

     /etc/mailcap
           [Option] System wide MIME type handler definition file, see The
           Mailcap files.  This location is part of the RFC 1524 standard
           search path, which is a configuration option and can be overridden
           via

     ~/mbox
           The default value for MBOX.

     ~/.mime.types
           Personal MIME types, see The mime.types files.

     /etc/mime.types
           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
           actually used path can be overridden via NETRC.

     /dev/null
           The data sink null(4).

   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.  This variable is only
           honoured when defined in a resource file, e.g., it is one of the
           INTERNAL VARIABLES.

     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!)

     Unless Mail is about to enter interactive mode syntax errors that occur
     while loading these files are treated as errors and cause program exit.
     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 ...]
           # E.g.: 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
     This feature is not available in v14.9.0, sorry! RFC 1524 defines a “User
     Agent Configuration Mechanism” which Mail [Option]ally supports (see HTML
     mail and MIME attachments).  It defines a file format 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
     “mailcap” files and the MAILCAPS environment variable that can be used to
     overwrite that (repeating here that it is not a search path, but instead
     a path search specification).  Any existing files will be loaded in
     sequence, appending any content to the list of MIME type handler
     directives.

     “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 also ignored.  All other lines form individual
     entries that must adhere to the syntax described below.  To extend a
     single entry (not comment) its line can be continued on follow lines if
     newline characters are “escaped” by preceding them with the reverse
     solidus character ‘\’.  The standard does not specify how leading
     whitespace of follow lines is to be treated, therefore Mail retains it.

     “Mailcap” entries consist of a number of semicolon ‘;’ separated fields,
     and the reverse solidus ‘\’ character can be used to escape any following
     character including semicolon and itself.  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
     content is ignored (removed).

     The first field defines the MIME ‘TYPE/SUBTYPE’ the entry is about to
     handle (case-insensitively, and no reverse solidus escaping is possible
     in this field).  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 defines the shell command which
     shall be used to “display” MIME parts of the given type; it is implicitly
     called the view command.

     For data “consuming” shell commands message (MIME part) data is passed
     via standard input unless the given shell command includes one or more
     instances of the (unquoted) string ‘%s’, in which case these instances
     will be replaced with a temporary filename and the data will have been
     stored in the file that is being pointed to.  Likewise, for data
     “producing” shell commands data is assumed to be generated on standard
     output unless the given command includes (one ore multiple) ‘%s’.  In any
     case any given ‘%s’ format is replaced with a(n already) properly quoted
     filename.  Note that when a command makes use of a temporary file via
     ‘%s’ then Mail will remove it again, as if the x-mailx-tmpfile,
     x-mailx-tmpfile-fill and x-mailx-tmpfile-unlink flags had been set; see
     below for more.

     The optional fields either define a shell command or an attribute (flag)
     value, the latter being a single word and the former being a keyword
     naming the field followed by an equals sign ‘=’ succeeded by a shell
     command, and as usual for any “Mailcap” content any whitespace
     surrounding the equals sign will be removed, too.  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.)

     edit  A program that can be used to edit a body or body part in the given
           format.  (Currently unused.)

     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, e.g., 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.

     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.

     copiousoutput
           A flag field which indicates that the output of the view command
           will be an extended stream of textual output that can be
           (re)integrated into Mail's normal visual display.  It is mutually
           exclusive with needsterminal.

     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.)

     nametemplate
           This field gives a filename format, in which ‘%s’ will be replaced
           by a random string, the joined combination of which will be used as
           the filename denoted by MAILX_FILENAME_TEMPORARY.  One could
           specify that a GIF file being passed to an image viewer should have
           a name ending in ‘.gif’ by using ‘nametemplate=%s.gif’.  Note that
           Mail ignores the name template unless that solely specifies a
           filename suffix that consists of (ASCII) alphabetic and numeric
           characters, the underscore and dot only.

     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.

     description
           A textual description that describes this type of data.

     x-mailx-even-if-not-interactive
           An extension flag test field — by default handlers without
           copiousoutput are entirely ignored in non-interactive mode, but if
           this flag is set then their use will be considered.  It is an error
           if this flag is set for commands that use the flag needsterminal.

     x-mailx-noquote
           An extension flag field that indicates that even a copiousoutput
           view command shall not be used to generate message quotes (as it
           would be by default).

     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-test-once
           Extension flag which denotes whether the given test command shall
           be evaluated once only and the (boolean) result be 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.

     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.  (Do not use this for asynchronous handlers.)  It is an
           error to use this flag with commands that include a ‘%s’ format, or
           in conjunction with x-mailx-async, or without also setting
           x-mailx-tmpfile or x-mailx-tmpfile-fill.

     x-mailx-tmpfile-keep
           Using the string ‘%s’ implies the three tmpfile related flags
           above, but if you want, e.g., x-mailx-async and deal with the
           temporary file yourself, you can add in this flag to forcefully
           ignore x-mailx-tmpfile-unlink.

     The standard includes the possibility to define any number of additional
     entry 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.  E.g., if a view command needs
     to specify the needsterminal flag, but the compose command shall not, the
     following will help out the latter (with enabled debug or an increased
     verbose level Mail will show information about handler evaluation):

           application/postscript; ps-to-terminal %s; needsterminal
           application/postscript; ps-to-terminal %s; compose=idraw %s

     In fields any occurrence of the format string ‘%t’ will be replaced by
     the ‘TYPE/SUBTYPE’ specification.  Named parameters from the
     ‘Content-type:’ field may be placed in the command execution line using
     ‘%{’ followed by the parameter name and a closing ‘}’ character.  The
     entire parameter should appear as a single command line argument,
     regardless of embedded spaces; 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).  Mail 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

           application/pdf; \
             infile=%s\; \
               trap "rm -f ${infile}" EXIT\; \
               trap "exit 75" INT QUIT TERM\; \
               mupdf %s; \
             x-mailx-async; x-mailx-tmpfile-keep

           application/*; echo "This is \"%t\" but \
               is 50 \% Greek to me" \; < %s head -c 1024 | 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
     The .netrc file contains user credentials for machine accounts.  The
     default location ~/.netrc may be overridden by the NETRC environment
     variable.  It is possible to load encrypted .netrc files by using an
     appropriate value in netrc-pipe.

     The file consists of space, tabulator or newline separated tokens.  Mail
     implements a parser that supports a superset of the original BSD syntax,
     but users should nonetheless be aware of portability glitches of that
     file format, shall their .netrc be usable across multiple programs and
     platforms:

     ·   BSD does not support single, but only double quotation marks, e.g.,
         ‘password="pass with spaces"’.
     ·   BSD (only?) supports escaping of single characters via a reverse
         solidus (e.g., a space can be escaped via ‘\ ’), in- as well as
         outside of a quoted string.
     ·   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, Mail 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”, Mail will always require these strict permissions.

     Of the following list of supported tokens Mail only uses (and caches)
     machine, login and password.  At runtime the command netrc can be used to
     control Mail's .netrc cache.

     machine name
           The hostname of the entries' machine, lowercase-normalized by Mail
           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 Mail
           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’.  Note that
           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

   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 support OAuth.  Because of this 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, 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 refreshed via the web periodically; in Kerberos / GSSAPI the
     local programs kinit(1) and kdestroy(1) offer user local control, the
     latter also while offline.

     Before being able to use OAUTHBEARER, some hurdles must be taken.  Using
     GMail as an example, an application (a simple name) needs to be
     registered, for which credentials need to be created.  This configuration
     step generates a “client ID” and a “client secret”.  These two strings
     need to be saved locally in a secure way.  For GMail these initial
     configuration steps can be performed via
           https://developers.google.com/identity/protocols/OAuth2.
     Thereafter access tokens can be requested, the program available for
     download do do this for a GMail account is
           https://github.com/google/gmail-oauth2-tools/blob/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
           $ # The last three are the actual token responses.
           $ # To refresh the granted token:
           $ python oauth2.py --user=EMAIL \
             --client-id=THE-ID --client-secret=THE-SECRET \
             --refresh-token=THE-REFRESH-TOKEN

     Mail does not (yet) offer the possibility to (lazy) expand aka run shell
     commandos which are embedded in variable content, or periodically run
     some command, therefore keeping an access token up-to-date from within it
     can only be performed by setting the hook on-main-loop-tick, or (for
     sending only) on-compose-splice.  For more on authentication please see
     the section On URL syntax and credential lookup.

   Not "defunctional", but the editor key does not work
     It can happen that the terminal library (see On terminal control and line
     editor, bind, termcap) reports different codes than the terminal really
     sends, in which case Mail will tell that a key binding is functional, but
     will not be able to recognize it because the received data does not match
     anything expected.  Especially without the [Option]al terminal capability
     library support one reason for this may be 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.  The verbose listing
     of bindings will show the byte sequences that are expected.

     To overcome the situation, use, e.g., the program cat(1), in conjunction
     with the command line 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.  E.g., the terminal this is typed on produces
     some false sequences, here an example showing 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
     file 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,
     e.g., the following lists 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.  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.  This man page is derived from “The Mail Reference
     Manual” that was originally written by Kurt Shoens.

     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, e.g., from within mail:
     ‘? eval mail $contact-mail’.  Including the verbose output of the command
     version may be helpful, e.g.,

           ? 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'’.

                                August 17, 2019