To add a shared mailbox, open Microsoft Outlook. Once Outlook is open, click on the 'File' button in the top right hand corner.
Clicking the 'File' button will open a new screen that allows you to modify the account settings. Click on the 'Account Settings' button and a new submenu will open. Click on the second 'Account Settings' button that is at the top of the menu.
A new windows should pop up entitled 'Account Settings'. Make sure that your account is highlighted in blue and click the 'Change' button as shown below.
On the next window, click the 'More Settings' button in the bottom right hand corner.
Click on the 'Advanced' tab and click the 'Add' button to add a new mailbox.
Add the name of the mailbox in the new window.
The new mailbox will now show in the list of additional mailboxes. Click 'Okay' at the bottom of the screen.
Click 'Next' at the 'Change Account' screen.
Then click 'Finish'. On the far right side of Outlook, in your list of accounts, the new mailbox will now be listed.