How to Relay Postfix SMTP on Ubuntu

Relay SMTP usually used by mail server with dynamic IP address. In this guide, I will show how to setup relay SMTP on Postfix.

Requirement:

• Postfix installed on Ubuntu
• SMTP server (you can use ISP’s SMTP)
• email address and password to login to SMTP server

How to:

1. Create password map file
   

   $ sudo nano /etc/postfix/sasl_passwd

   Type in your SMTP server, username (email address), and password into the file:

   smtp.colekcolek.com      email@colekcolek.com:password

2. Set permission to password map file, so it cannot be read by other user.
   

   $ sudo chown root:root /etc/postfix/sasl_passwd
$ sudo chmod 600 /etc/postfix/sasl_passwd

3. Create hash from map file (remember to do it each time you change your map file):
   

   $ postmap /etc/postfix/sasl_passwd

4. Edit Postfix config file
   

   $ sudo nano /etc/postfix/main.cf

   And make sure the following lines are exist.

   relayhost = smtp.colekcolek.com
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_auth_enable = yes
smtp_sasl_security_options = noanonymous

   If your ISP blocks outgoing port 25, you can choose to use alternative ports by modifying this line:

   relayhost = [smtp.colekcolek.com]:26

5. Restart Postfix
   

   $ sudo /etc/init.d/postfix restart