iXhash.pm is a plugin for SpamAssassin 3.1.0 and up (including 3.2, as far as I can tell). A version compatible with SpamAssassin 3.0 is provided as well.
...
- copy paste either 'ixhash.pm' or 'ixhash_v300.pm' into a file called ixhash.pm, depending on the SA version you plan to use the plugin with. 2. copy-paste the text contained in 'ixhash.cf' into a file called "ixhash.cf" 3. place ixhash.pm somewhere that is global r/x where SpamAssassin can access it - like /etc/mail/spamassassin. 4. edit the first line of ixhash.cf (loadplugin) to reflect where ixhash.pm is. 5. if you have to use the ixhash_v300.pm version, delete/comment the 'ixhash_timeout' line. This feature is not available with your version 6. copy ixhash.cf into /etc/mail/spamassasssin 7. run 'spamassassin -D < /some/mail/message', where '/some/mail/message' is a file containing an email. The copious output (on STDERR) should contain some occurences of 'IXHASH', showing you the plugin is being used. 8. restart spamd/amavisd/whateverDaemonUsesSpamAssassin
...