Outlook 2011 can’t import Outlook 2011-generated mbox mail archive files.
Outlook 2011 has a bug currently with importing Outlook 2011-generated mail archive files, where Outlook 2011 can export mail to .mbox files, but can’t then import the Outlook 2011-generated mbox files using its mbox import function. To fix this for one of my users (who needed to import mbox files given to her by another Outlook 2011 user), I came up with this workaround.
In this case, I was using Apple Mail and the procedure assumes that Apple Mail hasn’t been configured.
Here’s what needed to be done to fix it:
1. Open Apple Mail.
2. Set up a dummy account. (localhost was used for all requested server names.)
3. Import the mbox files using the following procedure:
A. In Mail, click on the File menu and select Import Mailboxes…
B. In the Import window, select Files in mbox format.
C. Select the mbox files to import.
4. Once imported, quit Mail
5. Open Outlook 2011.
6. Import the mbox files using the following procedure:
A. In Outlook, click on the File menu and select Import
B. In the Begin Import window, select Information from another application.
C. Select Apple Mail.
D. In the Import Items window, uncheck all except for Messages
7. Outlook will seem to freeze as it imports the messages.
8. If the On My Computer folders are hidden, you will need to unhide them (see here for details: https://derflounder.wordpress.com/2011/01/26/enabling-the-hide-on-my-computer-folders-checkbox-in-outlooks-general-preferences/ )
9. Find the Mail import folder.
10. Copy the imported mail into a new folder under the user’s Exchange inbox.
11. If you unhid the On My Computer folders, re-hide them.