Choosing A Port
First you want to decide on a port. Many use port 26 as the alternate SMTP port and CPanel recommends it, but several ISPs who do port 25 filtering also filter port 26, so it really isn’t a great choice. I personally recommend conforming (at least partially) to the RFC’s, so I decided to go with port 587 based on RFC4409.
Setting Up Exim To Listen On Your Chosen Port
Login to your Web Host Manager ( http://whatever.yourserver.com/whm ) and navigate to Service Configuration -> Service Manager. Scroll to the bottom and you will see an option for “Exim on another port”. Check this box and set it to the chosen port (in my case 587).
Open the ports in firewall too,