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.
Using the Active Directory Administrative Center I searched for Info and right clicked on the user. After clicking Properties I went to the Extensions page and then clicked on the Attribute Editor tab.
Changing the attribute
<not set> to
Created made the user visible to the SBS Console and allowed me to use the POP3 Connector on it.