Here is a Christmas present from Korey.  I hope you find it useful:

http://www.webmail.us/misc/blagr.php

Provides a window into our dnscache + rbldnsd system.  You can see which third-party spam blacklists use (we rsync them locally), and you can do lookups on IP addresses and domains that you think might be listed.

http://www.webmail.us/misc/spamrules.php

Provides a complete list of our spam filtering rules, along with description and score.  This list is auto-updated daily.