In trying to eliminate anything that could be preventing our only mobile device users device from working, I've come across one procedure listed in Microsoft documentation that is not available. The Exchange 2007 documentation refers to a Client Access tab in the Properties of a Users Mailbox. Specifically, this can be found in the TechNet Library bb124315. In a different section, a different procedure is refered to with basically the same heading, but no mention of the Client Access tab, bb123778. When I pull up my user's mailbox properties, there is no Client Access tab. Why is it missing? Is this related to not being able to sync the user's mobile device?

Are the users' in questions mailboxes on 2003 with a 2007 cas, or is it pure 2007? Have you got a default activesync policy applied?