It's *really* ment to be use from inside mutt... but to use it from a command
line you can do it like this:
mail2procmail < some.mail.letter

The needed lines to your muttrc is something like:
macro pager \Cf "|~/path/to/mail2procmail\n"
macro pager \Cf ":set pipe_decode\n|~/path/to/mail2procmail\n"

This will binds <ctrl>-f to execute mail2procmail... mail2procmail will
exec generateproc.pl to generate a file called ~/.procmail/m2proc.rc.
in your .procmailrc you should have something like
"INCLUDERC=~/.procmail/m2proc.rc" and everything should work.

WWW: http://www.tux.org/~timball/