Postfix is a free and open-source mail transfer agent (MTA) that routes and delivers electronic mail, intended as an alternative to the widely used Sendmail MTA. This is a simple guide on it which you will learn how to install and configure it.
This tutorial will show you how to build a powerful server with Debian. I'll describe everything you need to install and configure to get a production or development environment. Fifth, let's install and configure a mail server (Postfix, Devecot, and MySQL).