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://maildropl.listbot.com/

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