Q: Internet accounts pop up problem

hi

An email account I had access to has been deactivated since I left a university. I still want to be able to see all of my old emails which I have downloaded on my computer in the mail app (which is working fine and they are all there), but a little pop up keeps coming up and asking me for my password... like every 5 seconds after I click 'close' and never stops. I can't enter my password because the account doesn't actually exist anymore. But as I said, I still want to be able to see the emails (there are thousands of them) in my mail app. The only way I can stop it is by deactivating the account in the mail app, but this gets rid of the email inbox and I cant see the emails in the app.

How do I get rid of the pop up and keep my inbox in the mail app??

help!