SpamAssassin includes support for many of the bigger DNSBLs, with optimal scores (or at least, optimal as determined by the GeneticAlgorithm).
Support for these is built-in, and shipped in the default configuration.
All of the free BL services are enabled by default. However, note that if you're using mail-abuse.org, and you're installing SpamAssassin for site-wide use, you must license their services; mail-abuse.org is now only free for personal use.
FIXME: add a list of non-free tests that are enabled by default so admins can easily disable by setting scores to 0
Note that SpamAssassin still works very well without using these two services, however.
Live accuracy figures for most of the DNSBLs used in SpamAssassin, based on the Oct 2003 mail feed for one user, can be found here: http://taint.org/2003/11/07/184247a_mail.html
Other places to find out about DNS blacklists / blocklists:
- Dr. Jørgen Mash's DNS database list checker http://moensted.dk/spam/
- List of All Known DNS-based Spam Databases (blacklists) http://www.declude.com/junkmail/support/ip4r.htm
- Current Blacklist Comparison (note: no statistics for false positive rates) http://www.sdsc.edu/~jeff/spam/cbc.html
Note that it's extremely important to compare false positive rates (nonspam messages marked as spam), as well as spam hit-rates, when evaluating any anti-spam system, include DNS blocklists. (For example, a blocklist that returned a match for every single mail would 'catch all the spam', but would also mark every nonspam mail too.) Some of the above pages omit this information, so take with a pinch of salt.
[http://www.blocklisting.com/faq.html news.admin.net-abuse.blocklisting] is a newsgroup devoted to discussion of subjects related to the use, administration, and effects of blocklists in ameliorating the problem of unsolicited bulk email and other unwanted or abusive network traffic. It is also accessible through [http://groups.google.com/groups?group=news.admin.net-abuse.blocklisting groups.google.com].