This Error event indicates that the Microsoft Exchange Server 2010 transport routing engine can't determine the Active Directory site membership for the specified Exchange server. Routing has determined that a message should be delivered to the indicated server. However, the Active Directory site information for this server is not available in the referenced routing table. Therefore, routing is unable to deliver messages to recipients with mailboxes located on this server. This error may be caused by Active Directory replication latency.

To resolve this error, do one or more of the following:

• Take no action. The messages will be routed to the Unreachable queue and delivery will be retried when routing configuration changes. The Microsoft Exchange  Active Directory Topology service on the destination server is responsible for updating the Active Directory attribute that is used to determine the destination server's Active Directory site membership. When the Active Directory site information for the server is updated in routing tables, the messages will automatically be routed to the destination server.
  
  
• If you have been granted the correct permissions, you can force Active Directory replication to occur immediately. An Active Directory notification will cause the routing tables to be updated and any affected messages in the Unreachable queue will be resubmitted and routed to the destination server.
  
  
• Verify that the Exchange server specified in the error message text is functional and available on the network. Use the Ping or PathPing command-line tools to test basic connectivity. Use Ping to isolate network hardware problems and incompatible configurations. Use PathPing to detect packet loss over multiple-hop trips. For more information, see Microsoft Knowledge Base article 325487, How to troubleshoot network connectivity problems.
  
  
• Verify that the Exchange server that logged this event can communicate with one or more Active Directory servers available in the organization.
  
  
• Review other related Error and Warning events in the Application log. These related events may help you find the root cause of this error.
  
  
• If the recommended steps do not resolve this error, contact Microsoft Customer Support Services. For more information about how to contact support, visit the Microsoft Help and Support Web site.
  
  

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.