This category is for anti-spam programs that operate on mail servers. The difference between an anti-spam program running on a mail server and an anti-spam program operating on a mail client is that the filter running on the server can remove spam from everyone's mailbox at the same time, instead of from just one user's mailbox. Server-level programs are installed by a systems administrator, and individual users do not need to maintain them. Spam filters for a specific mail server (for example, writing filters for sendmail) are listed in the category devoted to that mail server. This category contains standalone software (and hardware) designed for spam filtering.
This category is specifically for server-level spam filters. Spam filters that operate on individual mailboxes (that is, mail filters that operate at the client level) belong generally in Computers/Software/Internet/Clients.

A spam filter that is a plug-in to a specific mail-reading program (or is a description of how to write filtering rules for that program) belongs in the category for that mail reading program. (For example, spam filters for Eudora belong in Computers/Software/Internet/Clients/Mail/Eudora.)

A spam filter that is a standalone application meant to be run by a client should go to Computers/Software/Internet/Clients/Mail/Windows/Tools/Anti-Spam (if it is a Windows program), or Computers/Software/Internet/Clients/Mail/ if it runs on any other operating system.

Spam filters that work with only one type of mail server should go in the category for that particular server; for example, Sendmail filter rules belong in Computers/Software/Internet/Servers/Mail/Sendmail. There are similar categories for a variety of mail servers in Computers/Software/Internet/Servers/Mail. If there is no category for the mail server your spam filters are written for, you can submit them here. Procmail filters go in Computers/Software/Internet/Clients/Mail/Unix/Procmail whether or not you think procmail is a client.

In addition, more general spam sites belong in Computers/Internet/Abuse/Spam. Hosted spam services belong in Computers/Internet/Abuse/Spam/Filtering