Outlook 2013 Hanging when adding Share Mailbox created in Office 365.

Hi There,  I've created a shred mailbox on my Office 365 Admin portal and assigned my user account full access to it.  I can open it normally through OWA, but when trying to add it to my Outlook 2013 client, (under "Account Settings>Advanced>Open Additional Mailboxes) it just sits there until I eventually force close outlook.

I've done research and it looks like i possibly need to make a CNAME change so this can be seen?  However, i'm, not sure what these details would be if needed.