Over the last week my server has been sending me Exim failure notices. Dozens a day that Exim has failed and was restarted the error contains the following:

Service Check Method: [tcp connect]

Failure Reason: Unable to connect to port 25

I have a secondary port set for SMTP as local ISP blocks 25 themselves. So all email is working.

CPanel/Centos box

If I remember correctly, you should be able to go to "Configuration/Service Manager" and then enable "Exim on another port" near the bottom and put the port number in.

If you've manually edited the exim config files, cPanel is oblivious to the change and is still checking port 25.