Email set up with IP address in admin system - programing. Asp.net

I recently had my server moved. My website has an automated email upon registering on the site and I need the site to have the correct IP, ie it is currently pointing to the old server.

I have tried to change this but there was an error sending the message so I am unsure if this is because the pop3 account is not set up or if there it is pointing to an incorrect port.

I think this is a fast simple job for someone who knows what they are doing.

I would also need advice on setting up a pop 3 local client email host.

Many thanks