Hi,
TO IMPORT AN MBOX FILE INTO OUTLOOK 2011 FOR MAC:
Follow this steps;
1. Copy the .mbox file to your Mac. A USB flash drive or an external hard drive is probably the easiest way to do that.
2. On your Mac, in Outlook 2011, select "Outlook 2011 -> File -> Import" menu command.
3. Select "Contacts or messages from a Text file" option.
4. Click on 'Continue' (Right arrow button).
5. Select "Import messages from an MBOX-format text file".
6. Click on 'Continue' (Right arrow button)
7. Select the MBOX file(s) you'd like to import. (If you are unable to select MBOX files because they are greyed out, please see the next section).
8. Click on "Import" button.
9. Click on "Finish" button.
10. You will find the imported mailboxes under "ON MY COMPUTER". (Note: If "ON MY COMPUTER" section is in collapsed mode, click on the triangle next to it to expand it).
Hope this helps..!!!