The safest to do this however is go to the
1. Make a note of the existing account name, pop and smtp addresses in the account ( paste it say, in notepad)
2.Navigate to C:\Users\your username/AppData/Local/Microsoft/WindowsMail.
3.Cut the entire contents of the folder and paste it in a new folder in C\: drive. Rename the folder as BackupMails
4. Restart windows mail. You will see it opening fine, but you must input all the account information like name, email, pop and smtp address and username\password.
5. Go to the Backup mails folder, browse to local folders and copy the folders EXCEPT the problematic folder ( Normally outbox)