This article may interest you, if when you try to send an email message in Outlook for Mac 2011 and the mails fails to send.
You receive this error message:
An unknown error has occurred in Outlook. A message in your Outlook could not be sent. The account which created the message could not be found.
Error code: – 17199
Also, you may receive an additional message that prompts you to re-enter your email password. Click Yes, and then enter your password.
To resolve this issue, Microsoft KB2405597 reccomends you try these steps:
1. Verify that you can connect on the web
2. Delete all emails in Outbox
3. Re-enter your user name and password