Disable an account in Apple Mail?

I have an email account under a domain that has been decommissioned. The domain still has an MX record, but its been disabled at the mail server. When someone tries to use the email address, they get a "550 Domain has been disabled" response back.

I cannot figure out how to disable the account. I've tried right clicking and "Take Offline", but that does not seem to help. Apple Mail still prompts me incessantly for a username and password. In addition, Apple Mail will no longer exit properly. It wants to throw a dialog for a password before it exits (that eventually requires a Force Quit).

I don't want to delete the account because I may need to refer to emails in the account.

How do I disable the account in Apple Mail?

(The operating system is OS X 10.8.5 (fully patched). Mail Version 6.6 (1510)).