spampd is a program used within an e-mail delivery system to scan messages for
possible Unsolicited Commercial E-mail (UCE, aka spam) content.

It uses an excellent program called SpamAssassin (SA) to do the actual message
scanning. spampd acts as a transparent SMTP/LMTP proxy between two mail servers,
and during the transaction it passes the mail through SA. If SA decides the
mail could be spam, then spampd will ask SA to add some headers and a report to
the message indicating it's spam and why. spampd is written in Perl and should
theoretically run on any platform supported by Perl and SpamAssassin.

WWW: https://github.com/mpaperno/spampd