Exchange Server 2003 relies heavily on the Microsoft Active Directory (AD) directory service for all its directory operations. Active Directory acts as a provider of information (mailbox, recipient, or address lists) and as a security guard to this information so that only authorized users and administrators have access. Coupled with new features found in Windows Server 2003, such as memory tuning, Volume Shadow Copy Service, remote access, and clustering, Exchange 2003 has increased performance and reliability necessary for the enterprise. A front-end and back-end server architecture adds additional scalability and reliability to a messaging environment. Whereas the front-end server provides an extra layer of security and handles SSL duties, the back-end server benefits users with an increased capability to process client requests and to load balance requests across a back-end server farm.