As spam levels increased quite a bit lately, I made a Gentoo Ebuild for the iXhash SpamAssassin plugin by Bert Ungerer / Heise iX, Germany.
So far, it’s available on bugs.gentoo.org only. In order to install it, download
and put it in your local Portage Overlay.
YMMV, but it performs really well on my server (particularly for German spam which is difficult to catch without). Don’t forget to adjust the according penalty scores to your liking, though!