Postfix: Using Gmail as a Relay Host

July 6th, 2012 Gmail , Linux , Ubuntu
I maintain several Linux servers at any given moment. Every server has postfix installed for sending emails, usually notifications or warning messages of some sort and most of these servers are professionally hosted allowing outbound emails with little to no configuration beyond installing postfix. However, my home server lies behind my ISP and they block all outbound emails citing SPAM as the reason. Regardless of their reasoning I had to find a workaround to allow me to send email notifications from behind my ISP. Well, it turns out this is rather painless with postfix and a Gmail account.

First, set up a Gmail account, note the user name and password for later.

Install postfix

$ sudo apt-get install postfix

Add the following to /etc/postfix/main.cnf

# Forward mail through Gmail
relayhost = [smtp.gmail.com]:587
smtp_use_tls = yes
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options = noanonymous
smtp_tls_CAfile = /etc/ssl/certs/Equifax_Secure_CA.pem

Create the file /etc/postfix/sasl_passwd and add the following:

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

Be sure to replace [username] and [password] with your account user name and password.

Modify file permissions and generate sasl_passwd.db

$ cd /etc/postfix
$ postmap sasl_passwd
$ chmod 600 sasl_passwd sasl_passwd.db

Restart postfix service

$ sudo service postfix restart

Send a test email

$ sudo apt-get install mailutils $ echo 'Success!' | mailx -s 'Test Message' [email_address]

Replace [email_address] with your email address to receive a test message.