To add a shared mailbox, you need to make sure you have been given permission to it and to any desired subfolders.
1. Open Outlook for Mac
2. Click "File"
3. Hover over "Open"
4. Click "Shared Mailbox…"
5. Type the name of the desired Shared Mailbox to add, then click "Add".
6. The system will verify if your account has permissions to add the mailbox. If so, the shared mailbox will appear in the left navigation under your primary mailbox.
7. Be sure to click the arrow next to the mailbox name to expand the folder and see all sub folders such as ‘Inbox’, ‘Sent’, etc.