This first section gives a brief introduction to Postfix, how it works, and describes how its behavior can be controlled.
Postfix is a modular mail transfer agent developed by IBM researcher Wietse Venema. It is free software and was released publicly for the first time in 1998 under the name VMailer. It is written in C and currently consists of about 105,000 lines of code (comments excluded), which makes it fairly small. It works on most non-historic variants of UNIX and Linux.
As a pure mail transfer agent, Postfix does not provide any service for allowing users to collect their mail via the POP or IMAP protocols. That task must be carried out by some other piece of software. The software discussed in this book for facilitating retrieval of mail from the host is Courier IMAP.
All official Postfix documentation, as well as the source code and links to third-party software and archives of the very active mailing list can be found at the Postfix website...