Anti-Spam SMTP Proxy
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.