Change Internet Service Provider Mail Settings

Today I changed my web hosting service provider, and with it, the email server for my business email address. I have entered the details of the new service provider in Email Accounts, but OS Mail refuses to connect, saying 'Unable to Verify Account Name or Password'.

I opened the Connection Doctor window and clicked 'Show Details'. And the details show that Mail is still trying to connect to my previous service provider (highlighted):

Where/how to change this? Please don't say 'clean reinstall', or else I'll simply stop using Apple Mail, I can live without it. I'm ok with removing specific registry keys or whatever they are.