mail/fdm - The NetBSD Packages Collection

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.