metamail - infrastructure for mailcap-based multimedia mail handling
[-b] [-B] [-c contenttype
...] [-d] [-e] [-E
] [-f from-name
] [-h] [-m mailer-name
[-p] [-P] [-r] [-s subject
] [-q] [-w] [-x] [-y] [-z] [file-name
program reads a "mailcap" file to determine how to
display non-text at the local site. Every mail-reading interface needs to call
metamail whenever non-text mail is being viewed, unless the mail is of a type
that is already understood by the mail-reading program. Metamail
consults the mailcap file(s) to determine what program to use to show the
message to the user.
At a site where all mail reading interfaces have been modified to call
for non-text mail, extending the local email system to handle
a new media type in the mail becomes a simple matter of adding a line to a
mailcap file. (Although this manual page will discuss only mail, metamail is
equally useful in adding multimedia support to news and bulletin board reading
programs, assuming those programs preserve the "Content-type" header
or some other indication of the content type of the messages.)
In general, users will never run metamail directly. Instead, metamail will be
invoked for the user automatically by the user's mail reading program,
whenever a non-text message is to be viewed. This manual page, therefore, is
directed not at end users, but at two categories of readers: those who are
adding metamail support to a particular mail-reading program, and those who
are adding lines to a mailcap file. The former need only to be concerned with
the command line syntax of metamail. The latter may ignore the command line
syntax, and need only be concerned with the mailcap file syntax, as described
in a later section.
Note: Metamail determines the type of a message using the
"Content-type" header, as defined in RFC 1049 and RFC-1341 (MIME).
However, using the -b and -c options, metamail can be made to work with mail
that is not in Internet format, including X.400 messages. Note also that
metamail automatically decodes mail that has been encoded for 7 bit transport
if the mail includes a Content-Transfer-Encoding header as specified by
RFC-1341. If data has been encoded via the "base64" encoding, it
will map CRLF to local newlines for textual data, but not for other data,
unless instructed otherwise by a "textualnewlines" field in a
When called with no options or arguments, metamail expects to receive an RFC 822
format message on its standard input. The following options can alter that
- This option tells metamail that the message is not in RFC 822 format, but
instead is only the body of the message (i.e. there are no message
headers). The use of -b requires the use of -c.
- This option tells metamail that the message is to be displayed in the
background, if it is non-interactive (i.e. it doesn't have the
"needsterminal" attribute in the mailcap file). It cannot be
used with -p or -P.
- -c <contenttype>
- This option tells metamail to use the specified content type rather than
the one in the headers, if any.
- This option tells metamail not to ask any questions before running an
interpreter to view the message. (By default, metamail always asks before
running almost any interpreter, if it is running in an interactive
terminal and the MM_NOASK environment variable is not set. However, it
does not ask about the content-type "text" -- that is, the
default value for MM_NOASK is "text,text/us-ascii")
- This option tells metamail to "eat" leading newlines in message
bodies. This is particularly useful for MH-format mail.
- -f <address>
- This option specifies the name of the sender of the message. Otherwise,
this is determined from the header, if possible. This information will be
placed in the environment to make it available to any interpreters called
- This option specifies that metamail is being used for printing a
message. In particular, this means that the normal mailcap
"command" field will not be executed, but instead the command
specified in the "print" field will be executed. (If there is
nothing in the print field, the mailcap entry will be ignored and the
search will continue for a matching mailcap entry that does have a print
field.) The -h option automatically turns on the -d option.
- -m <mailername>
- This option specifies the name of the mail program that called metamail.
This information will be placed in the environment to make it available to
any interpreters called by metamail.
- This option specifies that, if necessary, output should be shown to the
user one page at a time. By default, this will cause such output to be
piped through the "more" command, but the environment variable
METAMAIL_PAGER can be used to specify an alternative command to use. Note
that one should use -p rather than piping the output of metamail through a
pager, because some interpreters called by metamail might be interactive
rather than requiring pagination. Metamail can tell whether or not to use
a pager from information in the mailcap file. This option cannot be used
- This option is just like -p, except that it also causes metamail to print
"Press RETURN to go on" and await a RETURN after it has finished
with the message. This is intended for use only when metamail calls itself
recursively in a new terminal window created only for that purpose. This
option cannot be used with -B.
- This option tells metamail to be quiet. By default, metamail prints a few
key message headers (controllable with the KEYHEADS and KEYIGNHEADS
environment variables) and some other informative information, on stdout
before running the interpreter, but this behavior is suppressed with
- This option specifies that it is OK to run as root. By default, metamail
refuses to run if the real or effective user id is root. You can get the
same effect using the MM_RUNASROOT environment variable.
- This option specifies that the /usr/ucb/reset should be executed to reset
the terminal state, before any other I/O activity.
- -s <subject>
- This option specifies the subject of the mail message. By default, this
information is obtained from the headers. This information will be placed
in the environment to make it available to any interpreters called by
- This option tells metamail that instead of consulting a mailcap file to
decide how to display the data, it should simply decode each part and
write it to a file in its raw (possibly binary) format. Depending on the
circumstances in which it is called, metamail may derive the file name to
use from the message headers, by asking the user, or by generating a
unique temporary file name.
- This option tells metamail that it is definitely not running on a
terminal, no matter what isatty() says. This is necessary when metamail is
actually running on a pseudoterminal and isatty(3) returns TRUE but
there's really no terminal on which to interact with the user. The same
effect as -x can also be obtained with the environment variable
- This option tells metamail to try to "yank" a MIME-format
message from the body of the message. It is useful when a MIME-format has
been rejected by a mail delivery system that does not now how to format
the rejection in a MIME-compliant manner. (For the convenience of those
who can't control how metamail is called from their mail reader, this can
also be set with the MM_YANKMODE variable.) If you use yank mode on
messages that really ARE in MIME format, or on messages that do not
contain a MIME message in the body, the effects could be VERY strange. It
won't hurt you, but you won't see anything very useful, either.
- This option tells metamail to delete its input file when finished. The -z
option requires that a file name was given as an argument to metamail,
i.e. that it is not reading stdin.
- This option is intended to be used by metamail recursively, to turn off
the effect of the MM_TRANSPARENT environment variable. It should only be
used when the metamail program restarts itself in a terminal emulator
- File Name Arguments
- Any argument that does not start with "-" is interpreted as the
name of a file to read instead of standard input.
From time to time, metamail may tell you something like
**** Unrecognized mail type: 'smell-o-vision'. Writing to file
What this means is that your are trying to read a message that contains data
that is marked as being in "smell-o-vision" format, but that your
site has not yet configured metamail to properly display that type of data. In
the general case, such configuration is accomplished using the mailcap file
mechanism, as described in the next section.
For unrecognized types, metamail simply removes all header and encoding
information from the data, and writes it out to a temporary file. (If running
interactively, it will give you more alternatives -- writing it to a temporary
file, viewing it as text, or jus skipping it.) It is up to the user to delete
such files when he or she is through with them.
The primary purpose of the metamail program is to allow diverse mail reading
programs to centralize their access to multimedia information. If all the mail
reading programs call a single program to handle non-text mail, then only that
program needs to know about the diverse types of non-text mail that might be
The metamail program is made more flexible in this role through the mechanism of
one or more "mailcap" files. The purpose of the mailcap files is to
tell metamail what program to run in order to show the user mail in a given
format. Thus it becomes possible to add a new media type to all of the mail
reading programs at a site simply by adding a line to a mailcap file.
Metamail uses a search path to find the mailcap file(s) to consult. Unlike many
path searches, if necessary metamail will read all
the mailcap files on
its path. That is, it will keep reading mailcap files until it runs out of
them, or until it finds a line that tells it how to handle the piece of mail
it is looking at. If it finds a matching line, it will execute the command
that is specified in the mailcap file.
The default search path is equivalent to
It can be overridden by setting the MAILCAPS environment variable. Note:
Metamail does not actually interpret environment variables such as $HOME or
the "~" syntax in this path search.
The format of mailcap files is explained in the manual entry for mailcap(4).
Metamail has rudimentary built-in support for the emerging Internet standards
for non-ASCII data in mail headers. What this means is that such data will be
recognized, decoded, and sent to the terminal. This behavior may be more or
less reasonable, depending on the character set in the header data and the
capability of the user's terminal, but it will rarely be any worse than
showing such data in its encoded form.
- If set, this variable overrides "/tmp" as the name of the
directory in which metamail and associated programs will create temporary
files on UNIX.
- If MM_NOASK is set to "1", metamail will never ask the user for
confirmation before running an interpreter. Otherwise, MM_NOASK may be set
to a comma-separated list of type names (without white space) for which
the user does not desire confirmation. Thus, setting MM_NOASK to
"magicmail,audio" will cause the user not to be asked before
running interpreters for magicmail- or audio-format mail, but the user
will still be asked for all other types. (If the -d command line option is
given, MM_NOASK is set to 1 for spawned processes, allowing -d to work
- The KEYHEADS variable may be set to a colon-separated list of header
names, which are the only headers that metamail will print out. By
default, the behavior is as if KEYHEADS were set to:
If KEYHEADS is set to the empty string, no header are printed out. If it is
set to an asterisk ("*"), all headers are printed out.
KEYIGNHEADS The KEYIGNHEADS variable may be set to a
colon-separated list of header names, which are the headers that metamail
will not print out. This variable is only examined if KEYHEADS is not set.
If KEYIGNHEADS is set to the empty string, all headers are printed out. If
it is set to an asterisk ("*"), no headers will be printed
- If MM_NOTTTY is set to any nonzero value, metamail will assume that it is
not running in a terminal window. MM_NOTTTY implies setting MM_NOASK to 1.
If -z is given, MM_NOTTTY is set for spawned processes, allowing -z to
- This variable can be used to override the default path search for mailcap
- If set, this variable overrides "more" as the name of the
program to run to paginate output from an interpreter, when pagination has
been requested. Note that the normal "PAGER" variable is not
used because many pagers (notably the "less" pager) interfere
with the workings of termcap-based mail viewers.
- This variable is not actually used by metamail, but is used by most
metamail-compatible mail reading interfaces. If NOMETAMAIL is set to any
value, most mail reading interfaces will never call the metamail program,
effectively inhibiting all multimedia functionality.
- If MM_DEBUG is set to any value, metamail will produce slightly more
verbose output to tell what it is doing.
- If this variable is set to "1", metamail will produce even less
output than usual. In particular, it will suppress the
"Executing..." line unless MM_DEBUG is set.
Otherwise, this variable can be set to a comma-separated list of short
commands, and the "Executing..." line will be suppressed for
those commands only.
The default setting for MM_QUIET is "cat", which means that the
"Executing..." line is printed for all commands executed except
"cat". This makes text support look more natural without
sacrificing an understanding of what is going on in more complex
- Setting this variable to a non-zero value has the same effect as the -y
switch. Be sure to read the caveats attached to the description of -y
before you use it. Basically, the only time you would set MM_YANKMODE is
in order to re-enter a mail reader in which you can't control the way
metamail is called, just to read a single rejected MIME message that was
rejected by a mail agent that does not understand MIME. In such cases, you
should read that message, exit, and unset this variable.
- If this variable is set, metamail will reproduce the entire raw message on
stdout, and will open up a new terminal emulator window in which to do
something more intelligent. This option supports certain brain-dead mail
readers, such as mailtool, that actually depend on the output of the UNIX
"Mail" program being the same as the raw message in the
- If this variable is set, it will suppress the printing of character set
declarations when mail headers being printed contain text in this
character set. For example, if you set MM_CHARSET to
"iso-8859-8", it will suppress warnings when header output is
produced in that character set.
- Used to create a terminal window under the X11 window system.
- Used to create a terminal window under the SunTools window system.
- Used to create a terminal window under the old Andrew WM window
When metamail calls an interpreter specified in a mailcap file, it sets several
environment variables which can be used by the interpreter if desired:
- This variable is set to the full set of RFC822 headers, if any.
- This variable is set to the name of the mailer that called metamail, if
the -m option was used.
- This variable is set to the content type, as named by the Content-type
header or passed in via the -c option. If the content-type has a subtype
and parameters, these are also included in MM_CONTENTTYPE, e.g.
- This variable is set to an efficient one-line "caption" of the
message, typically including its sender and subject.
- This variable is set to a non-zero if the use of a pager has been
requested for long output (e.g. the -p switch was given.) If -p is given,
MM_USEPAGER is set for spawned processes, allowing -p to work recursively.
This option cannot be used with -B.
- This variable may be set to a string that is used to start a new terminal
window if necessary. The command to be executed in that window will be
APPENDED to this command. By default, this is set to something like
"xterm -e" if DISPLAY is set, or "shelltool" if
WINDOW_PARENT is set. Users of Sun's OpenWindows may wish to set
TERMINAL_CMD to "shelltool" if they prefer shelltool over
- If set to a non-zero variable, this will allow the metamail program to be
run by root, the same effect as the "-r" switch to
$HOME/.mailcap:/etc/mailcap:/usr/etc/mailcap:/usr/local/etc/mailcap -- default
path for mailcap files.
audiocompose(1), audiosend(1), ezview(1), getfilename(1), mailto-hebrew(1),
mailto(1), metasend(1), mmencode(1), richtext(1), showaudio(1),
showexternal(1), shownonascii(1), showpartial(1), showpicture(1), mailcap(4)
In a multipart/alternative body or body parts, some headers in the embedded part
that should be displayed may not be displayed. This will rarely be a problem.
Also, in a multipart/alternative, anything of type "multipart" or
"message" is considered to be a recognized part, regardless of the
recognizability of its contents. This might be a problem, only further
experience will tell.
The "textualnewlines" field in mailcap entries affects a global table
of exceptions. This means that if there is more than one mailcap entry for a
given content-type, and they have conflicting "textualnewlines"
settings, the wrong value may be used. I have been unable to conceive of a
situation where this would be a real problem, because it seems inconceivable
that a single content-type would ever require newlines to be treated in two
different ways, regardless of the environment.
The "%n" and "%F" mailcap fields do not work in
"test" clauses, because metamail does not perform sufficient
lookahead to do this right.
Copyright (c) 1991 Bell Communications Research, Inc. (Bellcore)
Permission to use, copy, modify, and distribute this material for any purpose
and without fee is hereby granted, provided that the above copyright notice
and this permission notice appear in all copies, and that the name of Bellcore
not be used in advertising or publicity pertaining to this material without
the specific, prior written permission of an authorized representative of
Bellcore. BELLCORE MAKES NO REPRESENTATIONS ABOUT THE ACCURACY OR SUITABILITY
OF THIS MATERIAL FOR ANY PURPOSE. IT IS PROVIDED "AS IS", WITHOUT
ANY EXPRESS OR IMPLIED WARRANTIES.
Nathaniel S. Borenstein