Mailagent allows you to process your mail automatically.  Given a set
of lex-like rules, you are able to fill mails to specific folders,
forward messages to a third person, pipe a message to a command or
even post the message to a newsgroup.  It is also possible to process
messages containing some commands.  The mailagent is not usually
invoked manually but is rather called via the filter program, which is
in turn invoked by sendmail.