fdm is a program to fetch mail and deliver it in various ways depending on a
user-supplied ruleset.  Mail may be fetched from stdin, IMAP or POP3 servers,
or from local maildirs, and filtered based on whether it matches a regexp,
its size or age, or the output of a shell command.  It can be rewritten by
an external process, dropped, left on the server, or delivered into maildirs,
mboxes, to a file or pipe, or any combination.

fdm is designed to be lightweight but powerful, with a compact but clear
configuration syntax.  It is primarily designed for single-user uses but may
also be configured to deliver mail in a multi-user setup.  In this case,
it uses privilege separation to minimise the amount of code running as
the root user.