Courier support for amavisd-new is maintained as a patch. This patch is distributed in the official amavisd-new tarball.
I wrote the original patch and do my best to keep it working with new versions of amavisd, but no more.
For more details about using amavisd-new with Courier, see the README.
I also have documentation on the check_mail function in amavisd-new. It was written around about amavisd-new 2.3.3, and has become rather out of date. This is not Courier-specific, but is the main MTA-independent function in amavisd-new: HTML DocBook XML
Some day, I might make use of the recently added support in Courier for filters changing the contents of a message, and to support header edits. I no longer run an MTA, other than for testing amavisd-new, so this is fairly low priority for me.
Martin Orr <firstname.lastname@example.org>