Acknowledgements

First, I would like to thank Stephen van den Berg, the creator of Procmail, and Philip Guenther, who has taken over development of Procmail in the last few years, for their wonderful tool. It is truly the friend of those who hate email spam and want it out of their lives. (It is also the friend of anyone who gets a lot of email.)

Second, I would like to thank the SpamBouncer development team for their contributions to improving the program. I especially want to thank Garen Erdoisa, who wrote the SpamBouncer 2.0 logging functions and has worked on a number of more minor features of the program. The SpamBouncer is slowly moving from being my baby to the work of a group of people. I expect it to become a much better program as a result.

Third, I would like to thank some fellow anti-spammers:

SPAM-L and SpamTools Mailing List participants. The readers of the SPAM-L and SpamTools mailing lists have been a constant source of help and ideas.
Participants in That Other Mailing List. I can't publicly thank the participants on one of the most useful email lists I read, since the list is private, but you know who you are.
Some specific fellow spam-fighters. There are too many spam-fighters I've worked with and learned from to mention more than a few, but I'd especially like to thank the following people (listed in alphabetical order, not order of importance):

Carl Hutzler. Carl Hutzler is a former head of the abuse department at AOL who remains active in fighting spam. He loathes spam, was proactive in stopping spam from AOL, was active in stopping spam to AOL, and communicates wonderfully well with the rest of us who fight spam. If AOL is the 2 ton gorilla of the ISP world, Carl is the guy who made that 2 ton gorilla an asset to the community. Carl, you're great. I hope AOL understands that a tenth as well as we in the anti-spam community do.
Chris Lewis. Chris is one of the first anti-spam activists, becoming one of the early anti-spammers on the Internet's venerable bulletin board system, the Usenet. He works for Nortel Networks in the IT department. (I think he's head of some part of it, if not the whole thing.) Over the years, he has remained a consistent voice against all types of abuses of the Internet, and a consistent source of information about what spammers are actually doing on a day-to-day basis. Thank you, Chris.
Steve Linford. Steve is the founder, maintainer, and chief cook and bottle washer at SpamHaus, although he has gathered quite a team of dedicated spamfighters around him. His persistent fight against spam through many years, even when under considerable legal and not-so-legal attacks by spammers, has encouraged me to keep at it when the spammers appear to be winning the fight. His relentless sanity in the face of the insanity of spam helps me to keep things in perspective. And his decision to keep SpamHaus a not-for-profit endeavor has multiplied the effect of his work and made it possible for others, like me, to make use of it in their own efforts. Thanks, Steve. I owe you. We all do.
Justin Mason. Justin is one of the developers for SpamAssassin, another anti-spam filtering program intended for systems that receive and filter significantly higher amounts of email than Procmail alone can handle. Unlike me, Justin is a programmer. (I program, but I'm a technical writer, not a software engineer, and anyone who looks at the SpamBouncer code knows it.) Justin has posted about and/or emailed me about a number of little features and ideas that have improved the SpamBouncer in all sorts of ways. One nice feature of the open-source, not-for-profit community is that we can cooperate on stuff like this. (It's especially nice when the competitor is better than I am at several important things.)
Anne Mitchell. Anne was the original attorney for MAPS, the first of the anti-spam rDNSBLs. After she left MAPS, she founded Habeas, an anti-spam company that focuses on identifying non-spam email and whitelisting it. After leaving Habeas, she founded the Institute for Spam and Internet Public Policy (ISIPP), a think tank for those working on legal and political solutions to the spam problem. Among other things, Anne first suggested to me that whitelisting needed to be a significant part of successful spam filtering. That led to the SpamBouncer's extensive whitelists, which have considerably reduced false positives and improved the efficiency of the program. She's a constant help in fighting spam on fronts that aren't technical, but are extremely important if the fight is to be won. Anne, you rock. Thanks.
Scott Hazen Mueller. Scott is the host of Abuse.net, nearly the first place any reasonable person stops when learning about spam and what to do about it. He is also on the board of directors for CAUCE and is active in the fight against spam in a million quiet and extremely useful ways. Thanks, Scott.
Suresh Ramasubramanian. Suresh founded CAUCE India, and runs the abuse department at Outblaze, one of the largest email service providers in the world. Suresh keeps me aware of the real issues and real complexities faced by ISPs and other large providers of internet services. He's also reasonable and possessing of good sense well beyond his years, even when he's expressing an opinion about a spammer in his usual inimitable manner. <ducking and running>

Fourth, I'd like to thank the participants in the Procmail Mailing List, who answered lots of often elementary questions when I was first learning to understand and use Procmail. I highly recommend the list for people who want to move beyond simply using the SpamBouncer into writing their own spam filters.

Finally, I'd like to thank one of the best sets of users anyone ever had. A number of users have contributed code and bug fixes to the SpamBouncer. Several feed me the take from spamtrap addresses, increasing the amount of spam I have to analyze and giving me a better view of what spammers are doing and what I need to do to catch their spam. And many, many of you report spam to me when the SpamBouncer misses it, or false positives when the SpamBouncer catches something it shouln't have, so that I know what needs fixing or updating first. You guys do a superb job keeping me up to date on what spammers are doing. I couldn't do it without you.

These filters are the result of almost a decade of work and learning about Procmail, spam, email, and programming. I hope the results will be as useful to others as they have been to me.