Trestlemail is a Mail Transport Agent that can run as an unprivileged Unix user. Many ISPs put all mail for a domain into a single multi-drop mailbox. It's often up to one person to go through the mail and forward it to the appropriate people.
Problem is, most ISPs charge per additional mailbox, and that can add up quick.
The combination of Fetchmail and Trestlemail completely solves these problems. And it does all this without requiring root privileges. Trestlemail runs automatically and transparently. It just requires an account on a machine that runs Fetchmail, Sendmail, and Perl. Once it's installed, Trestlemail is fairly easy to administer.