What is Postfix? It is Wietse Venema's mail server that started life at IBM research as an alternative to the widely-used Sendmail program. Now at Google, Wietse continues to support Postfix. Postfix runs (or has run) on AIX, BSD, HP-UX, IRIX, LINUX, MacOS X, Solaris, Tru64 UNIX, and other UNIX systems. It requires ANSI C, a POSIX.1 library, and BSD sockets. Postfix attempts to be fast, easy to administer, and secure. The outside has a definite Sendmail-ish flavor, but the inside is completely different. Multiple SMTP deliveries over the same TLS-encrypted connection. This reuses the existing tlsproxy(8) and scache(8) services. MySQL stored procedure support. Gradual degradation: in many cases a Postfix daemon will log a warning and continue providing the services that are still available, instead of immediately terminating with a fatal error. Postfix can set the execute bit on a queue file. If this does not work, then no mail will ever be delivered.