Free to individuals. Fights spam by putting a copyrighted haiku in the header that is only licenced (for a fee) to bulk mailers who respect codes of practice. This enables the identification of spam.

Provides advanced technologies and solutions to enhance the capabilities and manageability of e-mail.

A free e-mail forwarding and spam filtration service.

Enterprise level email protection and message management services.

POP3 service that blocks spam using sender verification methods.

Spam reporting service. Has been protecting the internet community since 1998. Automatically file spam reports with the network administrators who can stop unsolicited email at the source.

A mail filter, written in Perl, to identify spam using a wide range of heuristic tests on mail headers and body text. Free software. Can be used as a standalone mail filter, or from procmail.

Collaborative spam filtering network allowing users to report and filter out matching spam.