DNS blacklists are an integral part of any spam-fighting toolkit. That fact that many users on the Internet are...
updating them means that you get the benefit of blocking a spammer before the first piece of spam even hits you.
This chapter from the book The Anti-Spam Tool Kit by Paul Wolfe, Charlie Scott and Mike Erwin, explains what DNS blacklists are, how they work and how to implement them on a mail server. The chapter also discusses how to decide which DNS blacklist is the best to use for your organization's circumstances.