Where can I find out about how to integrate SpamAssassin with (some mail system)?
There's a whole load of integration glue out there, integrating SpamAssassin with virtually every mail system. To keep track of them, there are two places:
The "Where SpamAssassin is Used" page on the main website. This is now mostly superseded.
If you've come up with a new tool which supports SA, please post a note in this Wiki.