I just setup a laptop for IMAP access, tested the send and receive and everything worked just fine. I later went in and deleted and Exchange account that wasn’t used anymore and suddenly I was getting An Error Has Occurred (-17199). The solution was pretty simple. There was a message stuck in the “Folder on my Computer” Sent items folder from the Exchange days that still wanted to be sent through the Exchange system but couldn’t find the account. Deleting the message fixed the problem.