Generally, removing an email account on Outlook for Mac should not delete the messages in the On My Computer section. However, if the messages located in that section are important, creating a backup before deleting the account is a good idea.

Please be certain to follow these instructions closely. You may wish to get assistance in person from your local IT or through ESC (http://uoft.me/esc).

1. In Finder, open up the Go to Folder by pressing Shift + CMD + G.
2. Here, type or copy in ~/Library/Group Containers/UBF8T346G9.Office/Outlook/Outlook 15 Profiles
   
   
   
    
3. If you have more than one profile folder here, you may need to check which one you have been using. To check this, you can follow the first 5 steps of the article on configuring Outlook on a Mac.
4. Once you have determined which profile you have been using, you should select the folder, then copy and paste it within the same folder.
   
   
   
    
5. This may take a while depending on the size of the email profile.
6. Once it has copied the folder, you will see something like Main Profile and Main Profile copy.

7. Go to Finder. Open the Applications folder.
8. Ctrl+click or right-click Microsoft Outlook, and then select Show Package Contents. 
9. Open contents and select SharedSupport, and then launch Outlook Profile Manager.

 

           9. You'll see the Main Profile and the Main Profile copy in the window that appears.
          10. Right-click the newly created profile copy and select the circle icon at the bottom of the window. Select Set Default.

           11. If you re-open Outlook, it will go into the profile copy.
           12. You may now go through deleting the email account saved there.