I normally clean my sent files, and I noticed that one from last year is still there. I tried to delete, nothing. There is a long message that says boundary at the end. I searched for this file and found it in the finder. I deleted manually, and outlook started crashing. I rebuilt the identity and it fixed the annoying  "Microsoft Outlook must close" 

But the sent file is still there, showing in my outlook box, in spite of deleting it.

Is there a solution to get rid this once and for all.