Email messages do not route through Active Directory Site Links to different Active Directory sites

Consider the following scenario:

• You have an Active Directory Site Link which contains more than two sites. For example, the sites are�Default-First-Site-Name, U.S, and EU.
• One of these sites are listed alphabetically. For example�Default-First-Site-Name is listed first.
• There are no Exchange servers within these sites.

In this scenario, mail between Active Directory Domain Services (AD DS) and Active Directory directory service sites that use the Site Link for routing email messages fail if there is no direct connectivity between the source hub server and the destination server.�

To resolve this issue,�determine which Active Directory Site Link in your route contains an Active Directory Site that has no Exchange servers. After you have found which site does not have Exchange servers, follow any of these steps:

• Remove the site that does not have Exchange server from the site link.
• If the site is required for Active Directory Replication, you can create a new Active Directory Site Link with only Exchange servers. Set the Active Directory Cost for that site link to a larger value than the previous site link and set the Exchange Cost of the site link to a lesser value.

For more information about how to create, change and set site link cost values, visit the following TechNet pages:

For Windows Server 2008 and Windows Server 2008 R2:For Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with Service Pack 1, Windows Server 2003 with Service Pack 2: