Integrating Spam Assassin with your Mail Transfer Agent.
Documentation Pages on MTA Sites
Here are links to places that document how to integrate SA with your Mail Transfer Agent.
Wiki Markup Using\[http://www.exim.org Exim\] - \[http://www.exim.org Exim/exim-html-4.50/doc/html/spec_40.html Content Scanning\] with Spamassassin Documentation Page.