Shared Mailboxes

Hi Mark,

In OWA you have to open Manualy.

Open another person’s mailbox in a separate browser window in Outlook Web App
If you do not want to add the other person’s mailbox to your folder list in Outlook Web App, you can open the other person’s mailbox in a separate browser window.
Log in to your mailbox using Outlook Web App.
In the Navigation bar on the top of the Outlook Web App screen, click on your name. A drop-down list will appear. Click Open another mailbox.

https://support.office.com/en-us/article/Access-another-person-s-mailbox-a909ad30-e413-40b5-a487-0ea70b763081?ui=en-US&rs=en-US&ad=US

In Outlook 2016:

Note:  If your admin only recently provided you access to a shared mailbox, it may take a short time before the shared mailbox will automatically appear in your Outlook profile. If the shared mailbox doesn't automatically appear, you might need to restart Outlook to see it.

https://support.office.com/en-us/article/Open-and-use-a-shared-mailbox-in-Outlook-2016-and-Outlook-2013-d94a8e9e-21f1-4240-808b-de9c9c088afd