The qmail Handbook

fastforward is another Sendmail compatibility add-on. Sendmail uses a central alias database kept in a single file, usually /etc/aliases. qmail uses a series of dot-qmail files in /var/qmail/alias, one file per alias. If you're migrating to qmail and you've got a Sendmail-format aliases file that you don't want to convert, fast-forward gives qmail the ability to use the aliases file as-is.

Chapter 7, "qmail Configuration: Advanced Options," covers installing and configuring fastforward. fastforward was written by Daniel Bernstein, who maintains a Web page for it (http://cr.yp.to/fastforward.html).