How to send mail through Gmail On CentOS 7

How to send mail through Gmail On CentOS 7

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 send mail through Gmail On CentOS 7 with Postfix as a relay.

Requirements

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

Install Postfix

Install Postfix, the SASL authentication framework, and mailx are all installed.

yum -y install postfix cyrus-sasl-plain mailx

[root@ip-k8smaster ~]# yum -y install postfix cyrus-sasl-plain mailx
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
epel/x86_64/metalink                                                                                         | 9.1 kB  00:00:00
 * base: d36uatko69830t.cloudfront.net
 * epel: mirrors.aliyun.com
 * extras: d36uatko69830t.cloudfront.net
 * updates: d36uatko69830t.cloudfront.net
base                                                                                                         | 3.6 kB  00:00:00
docker-ce-stable                                               

Restart Postfix to detect  SASL framework .

systemctl restart postfix

Start Postfix  on boot.

systemctl enable postfix

[root@ip-k8smaster ~]# systemctl restart postfix
[root@ip-k8smaster ~]# systemctl enable postfix

Configure Postfix

Open the /etc/postfix/main.cf and add the following lines to the file.

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

Save the main.cf file and close the editor.

Configure Postfix SASL Credentials

Add the Gmail credentials for authentication. Create a "/etc/postfix/sasl_passwd" file and add following line:

 [smtp.gmail.com]:587 username:password

Replace valid Gmail credentials with  username and password values. The sasl_passwd file can now be saved and closed.

Create a Postfix lookup table from the sasl_passwd text file by running the following command.

postmap /etc/postfix/sasl_passwd

Now Restrict access to the sasl_passwd files .

chown root:postfix /etc/postfix/sasl_passwd*
chmod 640 /etc/postfix/sasl_passwd*

Reload the Postfix configuration.

systemctl reload postfix

Test 

Use the mail command to test the relay.

echo "This is Manas." | mail -s "message" xxxxx@yyy.com

The destination address should now receive the test message.

If you have issues like " Application-specific password required" , then you need to create app password and provide that in sasl_passwd file.

The logs can be viewed at "/var/log/maillog". The debug level can be increased by adding the following lines to the /etc/postfix/main.cf and restart postfix.

debug_peer_list=smtp.gmail.com
debug_peer_level=3

Check Postfix Config:

[root@ip-k8smaster ~]# postconf -n