Postfix

Postfix is an open source replacement for Sendmail, designed to be fast, easy to administer, and secure. It is for system administrators, organizations, and other users who need an alternative to Sendmail and place importance on straightforward administration, performance, and security. Its stated purpose is specifically to replace Sendmail; the available information does not identify a separate paid product that it replaces. Postfix should not be assumed to be identical to Sendmail. Although it is described as a Sendmail replacement, the available facts do not establish that it is a drop-in replacement, that it has exactly the same features, or that it can use every Sendmail configuration without changes. Users moving from Sendmail should therefore verify that Postfix meets their particular requirements rather than assuming complete compatibility.