Exchange Server Internet Mail Service

My Internet Mail Service on Exchange Server 5.5 is not running. When I try to start it manually I get a 2140 Error which relates to an internal NT error. I have checked the event log which reports Event IDs 4007 and 4020. Technet relates these errors to the service not binding to port25 of the proxy server.
I have followed all resolutions within Technet relating to this but still have the same 2140 error.

Does anyone know how I can check to see what is running on port 25 if the service cannot bind to it?

All ideas would be appreciated!