For those that do not know: XAMS is a sophisticated configuration for handling multiple virtual email domains, keeping all users in a strictly normalized MySQL database.
In contrast to things like vpopmail, it’s easy to set up, does not require patches to any software component involved and is extremely feature-rich.
XAMS was built by Oliver Siegmar, taking my initial idea (german. written von de.comm.software.mailserver), cleaning it up and adding a web interface
I posted my SpamAssassin configuration to the XAMS Mailinglist, so read it there.