Postfix: The Definitive Guide

Chapter 1. Introduction

Internet email history goes back as far as the early 1970s, when the first messages were sent across the Arpanet, the predecessor of today’s Internet. Since that time, email has been, and continues to be, the most widely used application on the Internet. In the olden days, email delivery was relatively simple, and generally consisted of moving mail files from one large host to another large host that served many users. As the Internet evolved and the network itself became more complex, more flexible tools were needed to move mail between different networks and different types of networks. The Sendmail package, released in the early 1980s, was designed to deal with the many variations among mail systems. It quickly assumed a dominant role for mail delivery on the Internet.

Today, most Internet sites use the SMTP mail protocol to deliver and receive mail messages. Sendmail is still one of the most widely deployed SMTP servers, but there have been problems with it. Sendmail’s monolithic architecture has been the primary cause of numerous security issues, and it can be difficult to configure and maintain.

Postfix was originally conceived as a replacement for the pervasive Sendmail. Its design eliminates many opportunities for security problems. Postfix also eliminates much of the complexity that comes with managing a Sendmail installation. Postfix administration is managed with two straightforward configuration files, and Postfix has been designed from the beginning ...