If you where trying to send an E-mail message using the Microsoft Outlook 2011 for Macintosh, and received the following 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". The following article will assist the user on how to resolve this error.

To resolve the error " An unknown error has occurred in Outlook" - Error code 17199", please follow these steps:

Step 1: Verify that you can connect on the web

First, test to see whether you can sign in by using the web-based application. For example, if you have a G-mail account, visit gmail.com, and then sign in. 

If you can sign in, go to the next step. If you cannot sign in, contact your email provider to obtain the correct user name and the password. 

Step 2: Delete all emails in Outbox

Open your Outbox and delete all outgoing emails then click Send/Receive. If the issue continues to occur, proceed to step 3. 

Step 3: Re-enter your user name and password

1. To re-enter your user name and password information, follow these steps
Open Outlook 2011.
2. Select Outlook then Preferences, this is located in the top navigation bar. Once the Preferences window appears select Accounts. 
3. On the left side of the window, select your email account.Enter the correct User name, your full email address, and the password.
4. Verify that the server name is correct by clicking the Advanced button located at the bottom of the window.
4. Click the red button in the upper-left corner of the window to save and close the window.