Postfix is another widely used MTA written by Wietse Venema. More information on Postfix is available online at http://www.postfix.org/. Unless otherwise noted, all configuration information in this section pertains to Postfix version 2.x.
Updating the Configuration
In a “standard” Postfix installation, the /etc/postfix directory is the home of all Postfix configuration files. main.cf contains the parameters that control the operation of Postfix. These settings include the SMTP clients and sender domains from which Postfix will accept mail. The clients and domains can be listed directly in the main.cf configuration file.
Whenever you modify any Postfix configuration file, including main.cf, you must reload the Postfix server by issuing ...