First check your disk permissions.
Second delete accounts in mail preferences.
Third reconstructs mailboxes
And if all else fails (1, 2 and 3 make them row), you can delete files from your library account (~ / Library / Mail / V2 / NOT WANT THE MAILBOX) and reviews the Accounts.plist file that is where accounts settings are saved. deletes the account appears where you want to delete (remember it is a XML is careful).