Email: Manually Add an Email Account to Outlook

In Outlook, click on File in the top left, then go to Account Settings (1), and then click on Account Settings (2). 

Then double-click on your email address, and then click on the More Settings button at the bottom of the new window. 

In the new window that opens, click on the Advanced tab, the click on Add... under the "Open these additional mailboxes:" section. 

Put in the mailbox you need in the Add Mailbox dialog box that pops up. Click OK, then Apply, then Next, then Close (closing out all the settings windows). Then, as long as it's spelled right, and you have access granted, it should be available in your Accounts list. If you don't immediately see it, close all Outlook windows and restart it.