How to add a shared Mailbox in the New Outlook

The "New Outlook" is not recommended at this time as some functionality is still missing. See Feature comparison between new Outlook and classic Outlook for a feature comparison.

It is recommended to switch back to “classic Outlook” if features in New Outlook are not working for you.

To access a Departmental/Shared mailbox that you have permission to:

It may already be available for you in the New Outlook. To see it, scroll to the bottom of your mail folders and expand the folder called Shared with me by clicking the > icon to the left of Shared with me:
If it isn't there, right click on your account name at the top of the folder listing and select Add shared folder or mailbox to open it:
Enter the email address of the shared mailbox and click Add:
The mailbox will be added under Shared with me:

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