Mail Avenger
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.

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Gonna have to do something when I bring the email accounts onboard the lan. Looks promising.