Adding mailbox to Outlook on Mac

On the Tools bar at the top click Accounts

Open

Select Advanced in the window that pops up

Open

Select Delegates from the next window that pops up

Click the + button on the bottom list

Search for the mailbox you wish to add by email address in the window that pops up

Click on the account you wish to add, I’m using Round Tower in this example, and then click Add in the bottom right.

The account should now show up in the bottom list

Click Server

Check the Sync shared mailbox checkbox if it is not checked

Click OK

Close out of the Accounts popup

Close Outlook

Launch Outlook and the shared mailbox should show up on the left side, click the > to expand the mailbox