Multiple SMTP Ports in Exim to bypass Telstra ISP
If you are running Exim mail manager and finding that mail just doesn't send. It might be because Telstra is your ISP and they don't like you sending except from their email. So they block port 25 to force that to happen. So you need to open up another port.
However what if as a server admin you open up another port (say port 26) and now all your customers who don't have Telstra as an ISP have to change their settings too - kind of inconvenient don't you think.
Here's the solution... open up both the old port 25 and another port (say 26) so that Telstra customers can use the new one, and all your other happy customers won't even know the difference, and can keep using 25.
If you are using Cpanel/WHM, go into Exim Configuration Manger, click advanced settings. Find the line that says
daemon_smtp_ports = 25 : 587 and edit it to include your new port number like this
daemon_smtp_ports = 25 : 26 : 587
Save and restart Exim and voila - good to go!