The postfix MTA

A number of open source e-mail servers exits, including Postfix, Sendmail, and Exim. In this unit, we will focus on Postfix, a powerful but relatively easy to configure MTA, which happens to be used by default in Red Hat Enterprise Linux 6.

Remember that Sendmail was the default MAT in Red Hat Enterprise Linux 5 and earlier.

Postfix is provided by the postfix RPM package, and is controlled by the postfix service script. It is a modular program made up of several cooperating programs, its components controlled by the master process.
The main configuration file for postfix is /etc/postfix/main.cf which may be edited using a text editor or with the postconf command. The postconf command may also be used to determine current and default configuration setting, either for all of Postfix or on an option-by-option basis.

By default, postfix only listen for incoming e-mail from localhost. To reconfigures Postfix to receive mail for local delivery sent from remote hosts, inet_interfaces = all must be set in /etc/postfix/main.cf.


When troubleshooting e-mail, a log of all mail-related operations is kept in /var/log/maillog, which includes information about rejections and successful deliveries. The mailq command (or postqueue –p) displays a list of any outgoing mail messages that have been queued. To attempt to deliver all queued message again immediately, you can run the postfix flush command (or postqueue –f); otherwise Postfix will attempt to resend them about once an hour until they are accepted or expire.

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