title: Anti-Spam SMTP Proxy
text: # 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.
  * Multi-threaded (Since version 2.x)
  * Platform independent (Written in Perl)
  