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The Directory Service Access (DSAccess) algorithm is changed in Microsoft Exchange Server 2003 Service Pack 2 (SP2). The new DSAccess algorithm may cause a larger load on global catalog servers in the local domain of the user. This issue occurs if many users have their mailboxes on Exchange servers that are located outside the users' Active Directory domain.
Versions of Microsoft Exchange Server before Exchange Server 2003 SP2
Typically, users of Microsoft Office Outlook 2003, Microsoft Outlook 2002, and Microsoft Outlook 2000, are referred to global catalog servers for directory access. In versions of Exchange Server before Exchange Server 2003 SP2, users are referred to global catalog servers that are located in the same site as the Exchange server that contains the users' mailboxes.
When user accounts and the Exchange servers that hold the user accounts' mailboxes are in different domains, Outlook users are referred to the global catalog server that is in the Exchange server domain. In this scenario, the Outlook users receive only read access to the global catalog server. Therefore, Outlook users cannot configure their delegates or any public distribution lists that the Outlook users own.
Exchange Server 2003 SP2
In Exchange Server 2003 SP2, the issue in which Outlook users receive only read access to the global catalog server is resolved by referring MAPI clients to global catalog servers that belong to the users' local domain. In an environment in which many users have their mailboxes on Exchange servers in other domains, there may be a significant change in the load on global catalog servers in the users' local domain.
This change in load occurs because referrals that were originally targeted to servers in the Exchange servers' domains are now all targeted to global catalog servers in the users' local domain. Therefore, the global catalog servers in the users' local domain may not be able to handle the additional load that is caused by the Outlook directory search request.
How to prevent an overload on global catalog servers in the local domain
To prevent an overload on global catalog servers in the local domain, estimate the change in load that may occur when you install Exchange Server 2003 SP2. Additionally, monitor the load before you install Exchange Server 2003 SP2. If it is required, you may manually control the referred global catalog server by changing the server configuration or the client configuration. For more information about how to do this, see the "References" section.
For more information, click the following article numbers to view the articles in the Microsoft Knowledge Base:
250570 Directory service server detection and DSAccess usage
319206 How to configure Outlook to a specific global catalog server or to the closest global catalog server