My wife’s parents are in town and they have signed up for Charter cable’s high speed internet access while they are up from Florida. Charter blocks port 25 except when relaying through their SMTP server. Right now they are using my webserver’s SMTP server to send mail, and we really didn’t feel like changing that since they will be switching back when they head back down. In order to circumvent this and make it so that they wouldn’t have to change their mailserver settings on their laptop again, I decided to open up a second port for SMTP.

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).

Hmm…Firewall?

I’m assuming you are running a firewall of some sort (I hope!), likely APF. To open the port in APF run a…

Assuming the file is located in /etc/apf/ you need to…

Find the line…

and add port 587 to it…

Viola!

There you have it! Pretty painless for the most part and easy enough for anyone who has WHM and SSH access to a CPanel server. Questions? Suggestions for another walkthrough? As always, ask away!

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