This guide is a step by step tutorial that details how to add an additional mailbox in Outlook 2011 for MAC
1. With Outlook 2011 open, click on the Tools menu at the top of the screen, then choose Accounts. Highlight your Exchange account, then click on Advanced.
3. Go to the Delegates tab and click the plus (+) sign under "People I am a delegate for:"
4. In the window that appears, search for the mailbox you are trying to add as a delegate. Once you have found the account, highlight the name and click OK.
After a brief period, the shared mailbox will appear as a folder in the View list on the left side of your Outlook window.