With iXhash we have a plugin for SpamAssassin, which computes MD5 checksums of fragments of the body of an e-mail and compares
them to those of know spam. As such it works very similar to Razor and DCC, which are already included in SpamAssassin.
The project is hosted by the same people who run the NiX Spam DNSBL: https://www.ranner.eu/2010/06/nix-spam-dnsbl-als-gute-alternative-fur-uceprotect-level-1/
iXhash can be simply installed from the FreeBSD ports tree: cd /usr/ports/mail/spamass-ixhash && make install clean