While setting up an install of SBS 2011 I was forced to rely on the POP3 Connector while I waited for Telus to change the internet connection to a static IP.
One of the email accounts of the company was a Shared Mailbox for the company info line that I created with an Exchange Management Shell command. Because the mailbox wasn't created using the SBS Console it wasn't visible in the list of Exchange Mailboxes the POP3 Connector could download to. Fortunately, it was an easy fix.