There are two ways to open a shared mailbox using Outlook on the web. One displays the shared mailbox under your primary mailbox, the other opens the shared mailbox in a separate browser window. You may want to try both methods and see which works best for you.
Adding the shared mailbox so it displays under your primary mailbox in Outlook on the web
This method is recommended if you want to monitor the email from your primary mailbox and the shared mailbox at the same time. In addition, after you complete this task, the shared mailbox and its folders are displayed in the left navigation pane each time you open Outlook on the web.
Right-click the word Folders in your primary mailbox in the left navigation pane, and then select Add shared folder:
The Add shared folder
dialogue box appears:
In the Add shared folder
dialogue box, type the name or email address of the shared mailbox.
Select the mailbox when it appears, and click Add
The shared mailbox displays in your Folder list in Outlook on the web. You can expand or collapse the shared mailbox folders as you can with your primary mailbox.
Note that if you want the "from" to show as that of the shared mailbox when composing or replying to emails, you will need to follow the steps found here.
Opening the shared mailbox in a separate browser window
We recommend that you use this method if you want to view and manage the email for the shared mailbox in its own browser window, or if you do not want to manually change the "from" address for new messages and replies.
On the Outlook on the web navigation bar, click on your profile image, or user initials in the top right corner and select Open another mailbox:
The Open another mailbox
dialogue box appears:
Type the email address of the other mailbox that you want to open, select it and click Add
Another Outlook on the web session opens in a separate window, allowing access to the other mailbox. You can bookmark this window if you want to return to it easily without having to follow these steps each time.
Using this method means that all new messages and any replies to messages in the mailbox will show the from address as that of the shared mailbox.