RFC 1343 (rfc1343) - Page 2 of 10
A User Agent Configuration Mechanism for Multimedia Mail Format Information
Alternative Format: Original Text Document
RFC 1343 Multimedia Mail Configuration June 1992
of a message is "foo" it can be displayed to the user via
the "displayfoo" program.
This approach means that, with a one-time modification, a
wide variety of mail reading programs can be given the
ability to display a wide variety of types of message.
Moreover, extending the set of media types supported at a
site becomes a simple matter of installing a binary and
adding a single line to a configuration file. Crucial to
this scheme, however, is that all of the user agents agree
on a common representation and source for the configuration
file. This memo proposes such a common representation.
Location of Configuration Information
Each user agent must clearly obtain the configuration
information from a common location, if the same information
is to be used to configure all user agents. However,
individual users should be able to override or augment a
site's configuration. The configuration information should
therefore be obtained from a designated set of locations.
The overall configuration will be obtained through the
virtual concatenation of several individual configuration
files known as mailcap files. The configuration information
will be obtained from the FIRST matching entry in a mailcap
file, where "matching" depends on both a matching content-
type specification, an entry containing sufficient
information for the purposes of the application doing the
searching, and the success of any test in the "test=" field,
if present.
The precise location of the mailcap files is operating-
system dependent. A standard location for UNIX is specified
in Appendix A.
Overall Format of a Mailcap File
Each mailcap file consists of a set of entries that describe
the proper handling of one media type at the local site.
For example, one line might tell how to display a message in
Group III fax format. A mailcap file consists of a sequence
of such individual entries, separated by newlines (according
to the operating system's newline conventions). Blank lines
and lines that start with the "#" character (ASCII 35) are
considered comments, and are ignored. Long entries may be
continued on multiple lines if each non-terminal line ends
with a backslash character ('\', ASCII 92), in which case
the multiple lines are to be treated as a single mailcap
entry. Note that for such "continued" lines, the backslash
must be the last character on the line to be continued.
Thus the overall format of a mailcap file is given, in the
modified BNF of RFC 822, as:
Borenstein