Mail filters

It is often useful to be able to split up incoming mail into several incoming folders, according to characteristics of the received mail (i.e. sender, subject, precedence, and so on). This is especially useful for users who are on multiple mailing lists and want to manage and prioritize their mail. This is what mail filters, such as procmail and slocal are made to accomplish.

Mail filters are usually set up by users individually, with a small amount sysadmin intervention sometimes involved. There are basically two approaches to mail filtering. One is to file the mail into folders after it has been received in the mail spool; MUAs such as VM and Pine can be set up to do this.

The other approach is to have your mail split up into separate spools as it is delivered. This is the approach that slocal (included with the MH mail system) and procmail use. Normally, the user sets up a .forward file which pipes incoming mail through the filter. For example, to use slocal, a user's .forward might look like this:

         "| /usr/local/mh/lib/slocal -user username"

Procmail is one of the better-known mail filtering systems. The sources can be found at ftp://ftp.informatik.rwth-aachen.de/pub/packages/procmail/"

For information on how to configure slocal and procmail see the slocal man page and the Mail Filtering FAQ.

Terms used: mail filter, MUA, .forward, procmail, slocal.