.TH METAMAIL 1 "Release 2" "Bellcore Prototype"
.SH NAME
metamail - infrastructure for mailcap-based multimedia mail handling
.SH SYNOPSIS
.ta 8n
\fBmetamail\fP	[-b] [-B] [-c \fBcontenttype\fP ...] [-d] [-e] [-E
\fBcontentencoding\fP] [-f \fB from-name\fP] [-h] [-m \fBmailer-name\fP]
[-p] [-P] [-r] [-s \fBsubject\fP] [-q] [-w] [-x] [-y] [-z] [\fBfile-name\fP]
.br
.SH DESCRIPTION
The
.I metamail
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.
.I 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
.I metamail
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 supp ort 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 ma y 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 mes sages.  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 mailcap entry.

.SH OPTIONS
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 expectation:
.TP 8
.B \-b
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.
.TP 8
.B \-B
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.
.TP 8
.B \-c <contenttype>  
This option tells metamail to use the specified content type rather than the
one in the headers, if any.
.TP 8
.B \-d 
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 varia ble 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")
.TP 8
.B \-e 
This option tells metamail to "eat" leading newlines in message bodies.
This is particularly useful for MH-format mail.
.TP 8
.B \-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 by
metamail.
.TP 8
.B \-h
This option specifies that metamail is being used for
.I
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 th e search will continue for a
matching mailcap entry that does have a print field.)  The -h option
automatically turns on the -d option.
.TP 8
.B \-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.
.TP 8
.B \-p
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 alterna tive 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 pag er from
information in the mailcap file.  This option cannot be used with -B.
.TP 8
.B \-P
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 cre ated only for that purpose.  This
option cannot be used with -B.
.TP 8
.B \-q 
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 thi s behavior is suppressed with -q.
.TP 8
.B \-r
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.
.TP 8
.B \-R
This option specifies that the /usr/ucb/reset should be executed to reset
the terminal state, before any other I/O activity.
.TP 8
.B \-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
metamail.
.TP 8
.B \-w
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, me tamail may derive the file name to
use from the message headers, by asking the user, or by generating a unique
temporary file name.
.TP 8
.B \-x 
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 intera ct with the user.  The same effect as -x can
also be obtained with the environment variable MM_NOTTTY.
.TP 8
.B \-y
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 th e 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 messag e in the body,
the effects could be VERY strange.  It won't hurt you, but you won't see
anything very useful, either.
.TP 8
.B \-z 
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.
.TP 8
.B \-T 
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 window.
.TP 8
.B File Name Arguments
Any argument that does not start with "-" is interpreted as the name of a
file to read instead of standard input.
.SH UNRECOGNIZED MAIL TYPES
From time to time, metamail may tell you something like

**** Unrecognized mail type:  'smell-o-vision'.  Writing to file
/tmp/metamail.1234 ****

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 configura tion 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.

.SH THE MAILCAP FILE(S)
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 kn ow about the diverse types of non-text mail
that might be received.

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 poss ible 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
.I 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

$HOME/.mailcap:/usr/local/etc/mailcap:/usr/etc/mailcap:/etc/mailcap:/etc/mail/mailcap:/usr/public/lib/mailcap"

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).

.SH NON-ASCII HEADER FIELDS
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, depe nding 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.
.SH ENVIRONMENT
.PP
.TP 8
.B METAMAIL_TMPDIR
If set, this variable overrides "/tmp" as the name of the directory in which
metamail and associated programs will create temporary files on UNIX.
.TP 8
.B MM_NOASK
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.  Thu s, 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 t o 1
for spawned processes, allowing -d to work recursively.)
.TP 8
.B KEYHEADS
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:

Date:From:Subject:To:CC:Content-Description

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.
.B 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 out.
.TP 8
.B MM_NOTTTY
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 work
recursively.
.TP 8
.B MAILCAPS
This variable can be used to override the default path search for mailcap
files.
.TP 8
.B METAMAIL_PAGER
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) interfer e with the workings of termcap-based
mail viewers.
.TP 8
.B NOMETAMAIL
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 f unctionality.
.TP 8
.B MM_DEBUG
If MM_DEBUG is set to any value, metamail will produce slightly more verbose
output to tell what it is doing.
.TP 8
.B MM_QUIET
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 circ umstances.
.TP 8
.B MM_YANKMODE
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.
.TP 8
.B MM_TRANSPARENT
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 act ually depend on the output of the UNIX
"Mail" program being the same as the raw message in the database.
.TP 8
.B MM_CHARSET
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 p roduced in that character set.
.TP 8
.B DISPLAY
Used to create a terminal window under the X11 window system.
.TP 8
.B WINDOW_PARENT
Used to create a terminal window under the SunTools window system.
.TP 8
.B WMHOST
Used to create a terminal window under the old Andrew WM window system.
.SH INTERPRETER ENVIRONMENT
When metamail calls an interpreter specified in a mailcap file, it sets
several environment variables which can be used by the interpreter if
desired:
.TP 8
.B MM_HEADERS
This variable is set to the full set of RFC822 headers, if any.
.TP 8
.B MM_MAILER
This variable is set to the name of the mailer that called metamail, if the
-m option was used.
.TP 8
.B MM_CONTENTTYPE
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.
"multipart/mixed; boundary=foobar".
.TP 8
.B MM_SUMMARY
This variable is set to an efficient one-line "caption" of the message,
typically including its sender and subject.
.TP 8
.B MM_USEPAGER
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.
.TP 8
.B TERMINAL_CMD
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 "shell tool" if WINDOW_PARENT is set.  Users of
Sun's OpenWindows may wish to set TERMINAL_CMD to "shelltool" if they prefer
shelltool over xterm.
.TP 8
.B MM_RUNASROOT
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 metamail.
.SH FILES
$HOME/.mailcap:/etc/mailcap:/usr/etc/mailcap:/usr/local/etc/mailcap --
default path for mailcap files.
.SH SEE ALSO
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)
.SH BUGS
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 b e 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 h ave 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.
.SH COPYRIGHT
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.
.SH AUTHOR
Nathaniel S. Borenstein
