Integrating Spam Assassin with your Mail Transfer Agent.
Here are links to documents on how to integrate SA with Mail Transfer Agent
[http://www.exim.org Exim] - [http://www.exim.org/exim-html-4.50/doc/html/spec_40.html Content Scanning] with Spamassassin Documentation Page.
[http://www.stalker.com CommuniGate Pro (CGP)] - Try CGPSA, available at http://www.tffenterprises.com/cgpsa/
Training
[http://www.gurulabs.com/training/GL275-Enterprise_Linux_Network_Services.php Guru Labs course GL275] - Feaures in-depth Spamassassin coverage (lecture and lab exercises) including MTA integration with Sendmail using milter and Postfix integration both after and before queueing