With Remote File Access in Exchange 2007, one can access files as read-only from anywhere using Outlook Web Access (OWA) or ActiveSync. The basic steps on how to configure Remote File Access are posted on TechNet. What follows here is an overview (including a few screenshots) of what to expect as far as configuration goes and some of the caveats to look out for before implementing Remote File Access. The Remote File Servers tab is configurable in both OWA and ActiveSync using the Exchange Management Console. Once those settings are stored in Active Directory, the CAS references Active Directory to detect what internal servers are accessible for Remote File Access. For an explanation of each setting available, refer to TechNet.
Full Article: Exchange Team blog