This Warning event indicates that a configuration domain controller that was specified in the Windows registry was not found in the Sites container in Active Directory. The configuration domain controller is a single computer that DSAccess selects to read and write information in the configuration naming context in Active Directory. A configuration domain controller should be a domain controller or a global catalog server.

This event can occur if one or more of the following conditions are true:

• The Microsoft Exchange Active Directory Topology service cannot locate the domain that contains the DNS server.
  
  
• The Active Directory Topology service cannot find the DNS name.
  
  
• The Active Directory Topology service cannot find a writable Naming Context in Active Directory.
  
  
• The Windows registry is configured to use an incorrect value. For example, the registry key or server name is not spelled correctly.
  
  

If other Exchange services start without a problem, this warning can be ignored. However, we recommend that you resolve this warning by doing one or more of the following:

• Make sure that the registry key and the configuration domain controller name are specified correctly in the Windows registry. This registry value is located as follows:
  
  HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeADAccess\Instance0\ConfigDCHostName
  
  

  Important:
  Create this registry key and specify a configuration domain controller name only if the automatically chosen domain controllers produce unwanted results. In such a case, find the problem, fix it, and delete the registry value so that the configuration domain controller is chosen automatically.

• Make sure that the configuration domain controller specified in the registry is registered correctly on the DNS server. For more information, see the following topics:
  
  
  • Troubleshooting Active Directory Related DNS Problems
    
    
  • DNS Support for Active Directory Tools and Settings
    
    
• In Active Directory Sites and Services, make sure that the configuration domain controller specified in the registry is listed under the Sites container.
  
  
• Check the Application log and the System log on the domain controller mentioned in the event description for any corresponding Warning or Error events.
  
  

For more information about directory service detection and DSAccess usage, see Microsoft Knowledge Base article 250570, Directory service server detection and DSAccess usage.

If you are not already doing so, consider running the Exchange tools created to help you analyze and troubleshoot your Exchange environment. These tools can help make sure that your configuration aligns with Microsoft best practices. They can also help you identify and resolve performance issues, improve mail flow, and better manage disaster recovery scenarios. To run these tools, go to the Toolbox node of the Exchange Management Console. To learn more about these tools, see Managing Tools in the Toolbox.