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How Exchange Server performs Active Directory LDAP queries

Exchange MVP Brien Posey describes the three services Exchange Server uses to perform Active Directory LDAP queries: DSAccess, DSProxy and the SMTP categorizer.

Because Exchange 2000, Exchange 2003 and Exchange 2007 all use Active Directory (AD) as a repository for mailbox...

configuration data, it is important to understand how Exchange Server and AD interact with each other.

When Exchange Server needs to extract information from Active Directory it does so by using Lightweight Directory Access Protocol (LDAP) queries. But Exchange Server does not perform these LDAP queries directly.

Instead, Microsoft has developed three special services that act as intermediaries between Exchange Server and Active Directory: DSAccess, DSProxy, and the SMTP categorizer.

These components are responsible for communicating with Active Directory and then providing Exchange Server with the information that it needs.

In this tutorial, Exchange MVP Brien Posey describes the role and purpose of these services in the Exchange Server and Active Directory infrastructure.

If you have any comments or questions about the information presented herein, please send an email to


 Home: Introduction
 Part 1: How the DSAccess service works in Exchange and Active Directory
 Part 2: How the DSProxy service works in Exchange and Active Directory
 Part 3: How the SMTP categorizer works in Exchange and Active Directory

Brien M. Posey, MCSE
Brien M. Posey, MCSE, is a Microsoft Most Valuable Professional for his work with Exchange Server, and has previously received Microsoft's MVP award for Windows Server and Internet Information Server (IIS). Brien has served as CIO for a nationwide chain of hospitals and was once responsible for the Department of Information Management at Fort Knox. As a freelance technical writer, Brien has written for Microsoft, TechTarget, CNET, ZDNet, MSD2D, Relevant Technologies and other technology companies. You can visit Brien's personal Web site at
This was last published in May 2007

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