Integrating Spam Assassin with your Mail Transfer Agent.
I would first take a look at IntegratedInMta (Sendmail, Postfix, Qmail)
Here are links to documents on how to integrate SA with Mail Transfer Agent
Training
- 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