The Anti-Spam SMTP Proxy (ASSP) is an open-source, Perl-based, platform-independent transparent SMTP proxy server.
Features Some ASSP's features are: Hidden Markov model spam filtering Bayesian spam filtering whitelisting Penalty Box (PB) trapping DNSBL/RBL (Realtime Blackhole Listing) URIBL (Uniform Resource Identifier Black Listing) Multi-level SPF (Sender Policy Framework) validation and blocking DKIM signing and validation DMARC validation and reporting SRS (Sender Rewriting Scheme) fix-up Session Delaying/Greylisting and connection response delaying Sender validation and recipient validation Multi-level attachment blocking (based on block lists or allow lists or content based executable blocking) As well as multiple RFC validation mechanisms. Multi-threaded (Since version 2.x) Platform independent (written in Perl)
See also
Transparent SMTP proxy SpamAssassin, popular open source spam filtering that uses razor and other techniques to detect spam. Qpsmtpd, a similar project
External links ASSP official homepage ASSP sourceforge project page Forum ASSP Wiki ASSP beta development site