In April of 1998, I write the first version of MailShield, which is an anti-spam/anti relay program for Windows and Unix. It has a built-in scripting language that I modeled after Perl (except that it's thread-safe, lightweight, and very fast). Chris Lewis at Nortel (author of the Usenet Cancelbot) was extremely helpful in working with me to include the best of the freeware world's anti-spam filters into MailShield, and people can edit or add to the rules by working with the perl-like rule language. Since it's release, I've added other kinds of useful mail features (not related to Spam) such as the ability to add a legal disclaimer to all outgoing mail, From: canonization, smart routing, among other things. For more information, check out the MailShield web site.