Some ISPs block outbound connections to servers on port 25 for SMTP. This is becoming less common, but still occurs on smaller or foreign ISPs. The reason they block this port is to prevent compromised client computers, especially botnets, from being used to send spam to other mail servers. So what do you do if you or a customer need to connect to your cPanel/WHM VPS or dedicated server to send mail through Exim?
You can open a secondary or even multiple SMTP ports for Exim to listen on and accept SMTP connections. To do this you will need to have root access to WHM and follow the following steps.
- Login to WHM as root.
- From the left scroll to the “Service Configuration” section.
- Click the “Service Manager” selection in that section.
- On the right you should now see the service manager options.
- Scroll down to the option labeled “exim on another port”.
- Check both check boxes (enable & monitor) and fill the box on the right with the port(s) you wish to have Exim listen on (ie. 26).
- Scroll down and click the “Save” button.
- Optional: You may need to configure the server’s firewall if you have one, to allow inbound access on the port of your choice.
Now you should be able to connect to your Exim SMTP server on the port of your choice now.