This document describes 5 easy steps to setup your Postfix email server as smarthost to relay on DNS Exit mail relay server for all email sending.
The mail relay service from dnsExit.com can be found at here
1. Create password maps file (it assigns username/passwords to specified mail servers). You can choose any name, let's say it is /etc/postfix/relay_passwd. It's content should be as follows:
relay.dnsexit.com USERNAME:PASSWORD
Note: Replace USERNAME and PASSWORD with your DNS EXIT mail relay username and PASSWORD.
2. Set proper permissions for that file:
# chown root:root /etc/postfix/relay_passwd
# chmod 600 /etc/postfix/relay_passwd
3. Create hash from maps file (remember to do it each time you change your maps file):
# postmap /etc/postfix/relay_passwd
4. Configure your /etc/postfix/main.cf:
relayhost = [relay.dnsexit.com]
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/relay_passwd
smtp_sasl_security_options =
Note: If your ISP blocks outgoing port 25. You can choose to use alternative SMTP ports by appending the port at the end:
relayhost = [relay.dnsexit.com]:26
5. Reload or restart your postfix:
# /etc/init.d/postfix restart