Adding another user or shared mailbox to your Outlook 2010.
1. In Outlook, choose the File tab, then the Info section (this should be the section you see by default). Choose Account Settings, then Account settings, again.
2. On the Account Settings window, choose the Data Files tab. Select your primary mailbox in the list (it will most likely have your name) and click the Settings... button.
3. In the Settings window, choose the Advanced tab and then click the Add... button.
4. In the Add Mailbox window, type in the name of the mailbox you want to open and click OK.
Note: If there are several mailboxes that match the name, you will be presented with another window asking you to pick the correct mailbox.
5. In the Settings window, you will now see your mailbox. Click OK.
6. In your navigation pane, you should now see the mailbox. Click the arrow that is immediately to the left of the name to expand it.