The ExternalURL value must be set

[This topic is intended to address a specific issue called out by the Exchange Server Analyzer Tool. You should apply it only to systems that have had the Exchange Server Analyzer Tool run against them and are experiencing that specific issue. The Exchange Server Analyzer Tool, available as a free download, remotely collects configuration data from each server in the topology and automatically analyzes the data. The resulting report details important configuration issues, potential problems, and nondefault product settings. By following these recommendations, you can achieve better performance, scalability, reliability, and uptime. For more information about the tool or to download the latest versions, see "Microsoft Exchange Analyzers" at]  

Topic Last Modified: 2010-11-16

The Microsoft Exchange Best Practices Analyzer Tool examines each Active Directory site that contains mailbox servers that are running Microsoft Exchange Server 2010. The Analyzer tool enumerates the ExternalURL values of the following locations on each Exchange 2010 and Microsoft Exchange Server 2007 Client Access server:

  • The Outlook Web App or Office Outlook Web Access virtual directory

  • The Exchange¬†ActiveSync virtual directory

  • The Offline Address Book virtual directory

  • The Web Services virtual directory

  • The Unified Messaging virtual directory

During this analysis, Exchange Analyzer uses the following logic to determine whether the ExternalURL values are set correctly:

  • If Exchange 2007 is running in the same site as Exchange 2010, the ExternalURL values must be unique.

  • If the ExternalURL value is set on an Exchange 2007 Client Access server, a unique ExternalURL value must be set on any Exchange 2010 Client Access server in the same site.

  • If Exchange 2007 is running in a site that does not contain any Exchange 2010 servers, Exchange 2007 may have a blank ExternalURL value. However, if the ExternalURL value is set to a value, the value must differ from any Exchange 2007 ExternalURL value.

A computer that is running the Client Access server role can act as a proxy for other Client Access servers in an organization. Doing this helps in an environment in which the following conditions are true:

  • The organization has multiple Client Access servers in different Active Directory sites.

  • Only one Client Access server is exposed to the Internet.

In this environment, the Internet-facing Client Access server can redirect requests to the appropriate Client Access servers in other Active Directory sites. The ExternalURL attribute value corresponds to the externally available URL for the particular virtual directory. For example, an ExternalURL attribute for the Outlook Web Access virtual directory may have a value of

If Exchange Analyzer determines that non-unique ExternalURL attribute values exist among Exchange 2010 and Exchange 2007 Client Access servers, a warning message is displayed. This message indicates that external users may be unable to access Exchange resources, such as Office Outlook Web Access, Exchange ActiveSync, and so on.

To use the Exchange Management Console to view the ExternalURL value

  1. On a server that is running Exchange 2010 , start the Exchange Management Console.

  2. Expand Server Configuration, and then click Client Access.

  3. In the work pane, click a server that is running the Client Access server role, and then click a tab that corresponds to the appropriate virtual directory in the bottom pane. For example, to view the ExternalURL value for the OwaVirtualDirectory location, click the Outlook Web Access tab.

  4. In the Name list, click the virtual directory. For example, click owa (Default Web Site).

  5. In the Actions pane, click the Properties link that corresponds to the particular virtual directory. For example, click Properties under owa (Default Web Site).

  6. Click the General tab, and then examine the URL that appears in the External URL box.

For More Information

For more information, see Understanding Proxying and Redirection.