Here is a good starting point: [http://www.stearns.org/doc/spamassassin-setup.current.html#sitewide ]
I want to run SpamAssassin for my large site. What specification of mail server do I need?: SitewideServerSpec
Where can I find out about how to integrate SpamAssassin with (some mail system)?: FindingIntegrations and IntegratedInMta
I posted a query about integrating SpamAssassin with (some mail delivery system), but nobody answered. Should I ask again??: AskingAboutIntegrations