http://spamassassin.apache.org/

This team is not officially recognized or endorsed by the SpamAssassin Project Management Committee or The Apache Software Foundation to which it reports.

There are basically three PPAs:
spamassassin-daily: Automatically built daily from SpamAssasin trunk, the latest development version.
spamassassin-test: Copied monthly from spamassassin-daily, for testing. Additional testers would be appreciated.
spamassassin-monthly: When a package makes it through a month in spamassassin-test without problems, it is copied here.

spamassassin-daily and spamassassin-test are not recommended for the timid, or those not actively reading the <email address hidden> mailing list, although SpamAssassin trunk has been remarkably reliable. spamassassin-monthly should be safe for general consumption.

(Copying is done by going into the source PPA, clicking "View package details", and then "Copy packages".)