Mutt supports RFC 1524 MIME Configuration, in particular the Unix specific format specified in Appendix A of RFC 1524. This file format is commonly referred to as the mailcap format. Many MIME compliant programs utilize the mailcap format, allowing you to specify handling for all MIME types in one place for all programs. Programs known to use this format include Netscape, XMosaic, lynx and metamail.
In order to handle various MIME types that Mutt can not handle internally, Mutt parses a series of external configuration files to find an external handler. The default search string for these files is a colon delimited list set to
$HOMEis your home directory.
In particular, the metamail distribution will install a mailcap file,
/usr/local/etc/mailcap, which contains some baseline