I recently released whitelister and uploaded it to debian (ITP#312309).

the major thing is the integration of the SPF as a new method to detect suspicious mail. It's nice, it blocks most of the spam coming from @hotmail.com addresses.

Moreover, the source repository is endly public. it's hosted on the subversion repository :

  svn co https://svn.aaege.org/mailtools/trunk/whitelister/
  svn co https://svn.aaege.net/mailtools/trunk/whitelister/

and we have a trac set up (the wiki docs are in french, sorry) with :