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.
- Valid Gmail or Google App credentials
Make sure Postfix, the SASL authentication framework, and
apt-get -y update apt-get -y --no-install-recommends install postfix mailutils libsasl2-2 libsasl2-modules
The Postfix install will prompt for several configuration settings. Use the following values for the corresponding setting:
- General type of mail configuration:
- System mail name: The preferred fully-qualified name of the mail server, e.g., mail.example.com
- SMTP relay host (blank for none):
Postfix will need to be configured to enable SASL authentication.
/etc/postfix/main.cf and add the following lines to the end of the file.
smtp_use_tls = yes smtp_sasl_auth_enable = yes smtp_sasl_password_maps = hash:/etc/postfix/sasl/sasl_passwd smtp_sasl_security_options = noanonymous smtp_sasl_tls_security_options = noanonymous
main.cf file and close the editor.
Create SASL Credential File
The Gmail credentials must now be added for authentication. Create a
/etc/postfix/sasl/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.
Generate Postfix Lookup Table
A Postfix lookup table must be generated from the
sasl_passwd text file by running the following command.
Restrict SASL File Permissions
It is advisable to restrict read and write access to the
chown -R root:postfix /etc/postfix/sasl chmod 750 /etc/postfix/sasl chmod 640 /etc/postfix/sasl/sasl_passwd*
Finally, start the Postfix service.
service postfix start
Test the Postfix Relay
echo "This is a test." | mail -s "test message" [email protected]
The destination address should receive the test message.
Troubleshoot Delivery Issues
It may be necessary to perform troubleshooting if the test message is not delivered successfully.
Start the Rsyslog service if not already running.
service rsyslog start
Note: Some container environments may not start Rsyslog by default.
Review the Maillog
maillog can be reviewed if the test message is not successfully delivered. Open another shell and run
tail while performing another delivery test.
tail -f /var/log/maillog
Enable Postfix Debugging
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 `/etc/postfix/main.cf“.
The Postfix configuration must be reloaded after updating the
service postfix reload
Remember to remove the debug settings when testing is complete. The verbose logs can have a negative impact on server performance.