Description:

Maildrop is a combination mail filter/mail delivery agent. Maildrop reads the
message to be delivered to your mailbox, optionally reads instructions from a
file how filter incoming mail, then based on these instructions may deliver
mail to an alternate mailbox, or forward it, instead of dropping the message
into your mailbox.

Maildrop uses a structured, real, meta-programming language in order to define
filtering instructions. Its basic features are fast and efficient. At sites
which carry a light load, the more advanced, CPU-demanding, features can be
used to build very sophisticated mail filters. Maildrop deployments have
been reported at sites that support as many as 30,000 mailboxes.

Maildrop mailing list:
http://lists.sourceforge.net/lists/listinfo/courier-maildrop

This version is compiled with support for GDBM database files, maildir
enhancements (folders+quotas), and userdb.