This Warning event indicates that the Microsoft Exchange Server 2010 transport routing engine could not calculate the route to the specified public folder hierarchy. Therefore, routing is unable to deliver messages to this public folder hierarchy. Public folders are stored on Mailbox servers. For more information, see Managing Public Folders

This warning may be caused by one of the following:

• No route to the store that hosts the public folder hierarchy exists.
  
  
• The server on which this event appears has not yet received configuration updates because of Active Directory directory service replication latencies.
  
  
• The public folder hierarchy is misconfigured.
  
  

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

• Use the Get-PublicFolderDatabase cmdlet in the Exchange Management Shell to verify that at least one database that hosts the public folder hierarchy exists.
  
  
• Verify the configuration of the public folder hierarchy.
  
  
• Take no action. The messages will be routed to the Unreachable queue and delivery will be retried when routing configuration changes.
  
  
• 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.
  
  
• Review the Application log and System log on your Exchange 2010 servers for related events. For example, events that occur immediately before and after this event may provide more information about the root cause of this error.
  
  
• Resolve your issue by using self-support options, assisted support options, and other resources. You can access these resources from the Exchange Server Solutions Center. From this page, click Self-Support Options in the navigation pane to use self-help options. Self-help options include searching the Microsoft Knowledge Base, posting a question at the Exchange Server forums, and others. Alternatively, in the navigation pane, you can click Assisted Support Options to contact a Microsoft support professional. Because your organization may have a specific procedure for directly contacting Microsoft Technical Support, be sure to review your organization's guidelines first.
  
  

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.