The Postfix mail server was written by Wietse Venema, author of Postfix and several other staple Internet security products, as an "attempt to provide an alternative to the widely-used Sendmail program. Postfix attempts to be fast, easy to administer, and hopefully secure, while at the same time being sendmail compatible enough to not upset your users."
Further information on postfix can be found at the Postfix home and in the Configuring and Securing Postfix.