This is mainly done to stop spamming from their network.
In this case we can use alternative port for SMTP service.
These are the steps on how to enable alternative port for the server.
1) Login into WHM.
2) Click on service manager.
3) Enter the Alternative SMTP Port in the box and apply changes.
“Run another copy of exim on port” After these steps process is not complete. But we need to add that alternative port in server firewall configuration in the section TCP_IN, TCP_OUT, UDP_IN, UDP_OUT.
Save the firewall configuration and restart firewall and you are done.!
If any feedback, queries are always welcome!