I am assuming you mean ~/username/Library/Mail, that should be where any mail files live.
What did you restore from? A Time Machine backup or other? In my experience, once you delete the account from Mail and all of the messages are gone, they're gone gone... even if the folder is still there for some reason.
You may want to try creating the account first and then importing the Mail files to that. You should also be able to import the messages (if they are still there) to another account in Mail other than the original IMAP account.
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