Opening a Shared Mailbox in Outlook on the Web
Go to www.office.com
Log into your own mailbox using the appropriate credentials (email address and password).
Select Outlook.
Click the profile icon/initials/avatar at the top right of the screen.
In the drop-down, select Open Another Mailbox…
Enter the email address, the Global Address List display name, or the resource number to open a shared mailbox. Select the shared mailbox in the list.
Click Open. The shared mailbox will now open in a new window.