Office 365 (Outlook 2016 for Windows) - Add Shared Mailbox to Outlook 2016
This article shows how a user can add a shared mailbox in their Outlook 2016 Windows client
1. Open up Outlook 2016 on Windows
2. Click on File then Open, followed by Open User's Folder...
3. Enter in the Shared Mailbox name or it's full e-mail address
4. Click on Ok
The shared mailbox should show up then on the left with all of your e-mail folders as well.