What Is DSProxy?

What Is DSProxy?
DSProxy is the Exchange 2000 component that provides an address book service to Microsoft Outlook® clients. DSProxy is implemented as a DLL file named DSPROXY.DLL. DSProxy has two functions:
• To emulate a Messaging Application Programming Interface (MAPI) address book service, and proxy requests to an Active Directory server
• To provide a referral mechanism so that Outlook clients can directly contact Active Directory servers
Although its name implies that it provides proxy services only, DSProxy provides both proxy and referral services. MAPI clients running Outlook 2000 Service Release 1 (SR-1) and earlier versions (including Outlook 2000, Outlook 98, Outlook 97, and the Exchange 5.0 client) use the proxy functionality. These earlier clients were designed with the assumption that each Exchange server contains a directory service. This is no longer true in Exchange 2000. Therefore, DSProxy emulates a directory service so that these earlier clients can continue to function. In actuality, however, the Exchange 2000 server forwards the requests to Active Directory.
Later versions of Outlook, such as Outlook 2000 (SR-2 and later) and Outlook 2002, are designed with the assumption that Exchange 2000 does not have its own directory service. After DSProxy refers one of these later clients to a global catalog server, the client communicates directly with Active Directory.
DSProxy obtains its list of working global catalog servers from DSAccess, but it does not route its queries through DSAccess. This is because DSProxy uses the Name Service Provider Interface (NSPI) to submit MAPI address book lookups. DSAccess handles only LDAP queries.