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