If you want to add an additional mailbox to Outlook, e.g. a shared mailbox for your team to view alongside your regular Inbox, then follow the following instructions. It’s not intuitive, requires an understanding of the context of what you’re actually doing in Microsoft lingo, i.e. You are adding an additional Mailbox to your existing Outlook Profile, not adding an Additional Mailbox to Outlook per se, (which is done outside of Outlook via the Mail icon in Control Panel and effectively creates an Additional Outlook Profile which you’ll be prompted to choose from each time you subsequently start Outlook).
Tools, Account Settings
Highlight your Account, and click Change (the bit that isn’t obvious / intuitive in my opinion).
Click on More Settings in the lower right hand corner.
The Mailboxes dialog appears and may well be blank. Click Add to add additional mailboxes. You’ll likely need to know the name of it.
The additional mailbox will now be added to the folders treeview pane in Outlook in your existing profile.