RFC 1524 (rfc1524) - Page 2 of 12

A User Agent Configuration Mechanism For Multimedia Mail Format Information

RFC 1524             Multimedia Mail Configuration        September 1993


   example, that if the content-type 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.





Borenstein