Outlook Web Access is not available for this mailbox. If the problem continues, contact technical support for your organization and tell them the following: The Client Access server %1, running Microsoft Exchange version %2, attempted to find a Client Access server to proxy Outlook Web Access traffic for mailbox %3. The service discovery failed in looking up the Client Access server in the target Active Directory site.Additional information: %4.

This Warning event indicates that the computer that is running the Client Access (CAS) server role could not determine the Client Access server that should handle a Microsoft Office Outlook Web Access request. Specifically, it could not determine whether the request should be processed by the local Client Access server, or if it should be proxied or redirected to a Client Access server in a different Active Directory site. Therefore, the mailbox specified in the event description could not be accessed through Outlook Web Access. This event may be caused by one or more of the following:

• The Client Access server cannot verify the location of servers that are running Microsoft Exchange Server in Active Directory sites.

• The Client Access server cannot verify the links between the Active Directory sites.

• The Client Access server cannot access required Exchange Server virtual directory configuration data from Active Directory.

• The Client Access server that accepts Outlook Web Access proxy or redirection requests is not in the same Active Directory site as the computer that is running the Mailbox server role.

For more information about Outlook Web Access proxying and redirection, see Understanding Proxying and Redirection.

To resolve this error, take one or more of these steps:

• If this occurs frequently, check network connectivity between the Client Access Server and domain controllers. 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.

• Make sure that the InternalUrl of the Outlook Web Access virtual directory exists and that it matches the fully qualified domain name (FQDN) of the local CAS server.

If you are not already doing so, consider running the tools that Microsoft Exchange offers to help administrators analyze and troubleshoot their Exchange environment. These tools can help you make sure that your configuration is in line with Microsoft best practices. They can also help you identify and resolve performance issues, improve mail flow, and better manage disaster recovery scenarios. Go to the Toolbox node of the Exchange Management Console to run these tools now. For more information about these tools, see Toolbox in the Exchange Server 2007 Help.