How to configure Postfix relay in Centos 7

What is Postfix Relay ?

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. In this post we 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.

Basic Requirements :

  • CentOS 7 or Red Hat Enterprise Linux 7
  • Valid Gmail or Google App credentials

Our Scenario :

Server Name –

IP –

Configuration :

Step 1 : Install the packages like : Mailx, Postfix & SASL Authetication framework.

[#] yum -y install Postfix mailx cyrus-sasl-plain 1

Step 2 : Postfix will need to be restarted before the SASL framework will be detected.

[#] systemctl start postfix

[#] systemctl restart postfix 


Step 3 : Postfix should also be set to start on boot.

[#] systemctl enable postfix


Step 4 : Open the /etc/postfix/


Now install the following lines at the end of the file.

myhostname =

relayhost = []: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


Step 5 : Configure the Postfix SASL Credentials

In this scenario we are using gmail as a postfix relay, so gmail credentials must now be added for authentication. Create a /etc/postfix/sasl_passwd file and add following line:

 []:587 username:password



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.

[#] postmap /etc/postfix/sasl_passwd


Access to the sasl_passwd files need to be restricted for the security purpose.

[#] chown root:postfix /etc/postfix/sasl_passwd*


[#] chown 640 /etc/posfix/sasl_passwd*


Now  reload the Postfix configuration.

[#] systemctl reload postfix


Step 6 : Now we will the test by sending the test mail to email id

Use the mail command to test the relay.

[#] echo ” this is a test mail.” | mail -s “test message”


The destination address should receive the test message.

The 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 /etc/postfix/

The Postfix configuration must be reloaded after updating the file.

[#] systemctl reload postfix.

                                   !!!!!!!!!!!!!!! Postfix Relay Successfully Completed !!!!!!!!!!!!!




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