SPAMbaffle

Fully configurable SPAM/virus filter for qmail servers. Set up in five minutes. Free trial version download. Each user may set up their own filtering rules and/or use global rules. Filter any header, the body, attachment filenames, and MIME types. Bounce or drop blocked messages. Use custom bounce messages to tell non-SPAMmers how to get email through in case of false positives, or to alert people infected with worms that they need to disinfect. Full version: $70 per server or $175 per company.