Other sites related to filtering spam (such as software to permit a mail client to filter spam, or web services that offer spam filtering) should be submitted to the appropriate category at Computers/Internet/Abuse/.
This category contains sites that maintain spam blacklists. Some of these blacklists are services that can be used to filter e-mail, and other blacklists are simply lists of spam-friendly ISP's and companies. Blacklists are distinct from spam filters; blacklists provide information about known spammers, but do not by themselves prevent spam from being received. Filters are programs that prevent a user from seeing spam (possibly by using a blacklist.)