Mailing-list managers differ primarily in the design and range of these secondary features. Unfortunately, the format for sending commands to mailing-list request robots is not standard. Some expect commands in the subject line, some ignore the subject line and expect commands in the message body. There is a rather comprehensive list of such packages on the Web. A mail filter is a program that sits between your local delivery agent and you, automatically dispatching or rejecting mail before you see it.
Mail filters have a number of uses.
The most important are spam filtering, dispatching to multiple mailboxes by topic or sender, and auto-answering mail. Typically, you set up mail filtering by putting a program alias for the filter program in your .forward file, and writing a file of filtering rules. The format and location of the filter rules file varies between filter programs. As these names imply, it is an obnoxious form of advertising that stuffs your mailbox with form letters. Spam tends to be both verbose and illiterate.