Postfix is a flexible mail server that is available on most Linux distribution. Though a full feature mail server, Postfix can also be used as a simple relay host to another mail server, or smart host. This tutorial will describe how to configure Postfix as a relay through Gmail.
Simple Authentication and Security Layer (SASL) is a standard authentication framework supported by many services including Postfix.
- CentOS 7 or Red Hat Enterprise Linux 7
- Valid Gmail or Google App credentials
Make sure Postfix, the SASL authentication framework, and
mailx are all installed.
yum -y install postfix cyrus-sasl-plain mailx
Postfix will need to be restarted before the SASL framework will be detected.
systemctl restart postfix
Postfix should also be set to start on boot.
systemctl enable postfix
/etc/postfix/main.cf and add the following lines to the end of the file.
myhostname = hostname.example.com relayhost = [smtp.gmail.com]:587 smtp_use_tls = yes smtp_sasl_auth_enable = yes smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd smtp_tls_CAfile = /etc/ssl/certs/ca-bundle.crt smtp_sasl_security_options = noanonymous smtp_sasl_tls_security_options = noanonymous
myhostname parameter is optional. If the hostname is not specified, Postfix will use the fully-qualified domain name of the Linux server.
main.cf file and close the editor.
Configure Postfix SASL Credentials
The Gmail credentials must now be added for authentication. Create a
/etc/postfix/sasl_passwd file and add following line:
The username and password values must be replaced with valid Gmail credentials. The
sasl_passwd file can now be saved and closed.
A Postfix lookup table must now be generated from the
sasl_passwd text file by running the following command.
Access to the
sasl_passwd files should be restricted.
chown root:postfix /etc/postfix/sasl_passwd* chmod 640 /etc/postfix/sasl_passwd*
Lastly, reload the Postfix configuration.
systemctl reload postfix
Test the Relay
echo "This is a test." | mail -s "test message" [email protected]
The destination address should receive the test message.
Troubleshoot Delivery Issues
maillog can be reviewed if the test message is not successfully delivered. Open another shell and run
tail while performing another test.
tail -f /var/log/maillog
If there are not enough details in the
maillog to determine the problem, then the debug level can be increased by adding the following lines to the
The Postfix configuration must be reloaded after updating the
systemctl reload postfix
Remember to remove the debug settings when testing is complete. The verbose logs can have a negative impact on server performance.