Set up Outlook to Open a Shared Mailbox as a Second (or third, etc.) Mailbox

From Outlook menu, choose Tools > E-mail Accounts
Select View or Change existing e-mail accounts option and click Next
Select the Microsoft Exchange Server account and click Change
Click the More Settings... button.
Click the Advanced tab.
Click the Add button on the Advanced tab.
On the Add Mailbox dialog, enter the exact display name of the mailbox to open and click OK.
Click OK at the bottom of the Advanced tab.
Click Next on the E-Mail Accounts window.
Click Finish on the E-mail Accounts window.
You should now see the account you entered in your list of accounts from Outlook.