macOS | Outlook for Mac

These steps assume the following:

A shared mailbox has been created in the Microsoft Exchange/Office 365 system and you have been granted rights to access the resource.
The shared mailbox has not been migrated to Office 365

Open Outlook for Mac
Navigate to Outlook > Preferences > Accounts
Select the + then New Account...
Enter the email address of the shared mailbox you want to connect to, then select Continue
If your web browser opens to a Google page, close or minimize it.
Then, in the "Set Up Your Email" window, select Not Gmail?
Select Exchange
Enter your Andrews email address and password, then select Continue.
No need to enter Server information.
If prompted with the following message, select Always use my response for this server, then select Allow
To add another shared mailbox, select Add Another Account. Otherwise, select Done
Back in the Accounts window, select the account you just added, then select Advanced
Select Sync shared mailbox (Restart Outlook for the change to take effect)
When Outlook is restarted, the shared mailbox will appear.