Mail Avenger is a highly-configurable, MTA-independent SMTP server daemon. It lets users run messages through filters like ClamAV and SpamAssassin during SMTP transactions, so the server can reject mail before assuming responsibility for its delivery. Other unique features include TCP SYN fingerprint and network route recording, verification of sender addresses through SMTP callbacks, SPF (sender policy framework) as a general policy language, qmail-style control over both SMTP-level behavior and local delivery of extension addresses, mail-bomb protection, integration with kernel firewalls, and more.

http://www.mailavenger.org/

-- LucaGibelli - 10 Feb 2007