Microsoft Exchange Server 2007 introduced that the Edge Transport server role can use the hosts file for name resolution to the Hub Transport server role. However, messages from an external server to a Hub Transport server may be queued on an Edge Transport server. Additionally, if you open the Queue Viewer from the Exchange Management Console, you find that the status of the queued messages are "451 4.4.0 DNS Query Failed" . This problem occurs when the following conditions are true:
The hosts file of the Edge Transport server is configured with the right entries for the Hub Transport server.
The Edge Transport server has no DNS server configured.
The internal send connector is configured by using "--” domain and the SmartHostDelivery .
This problem occurs because Exchange Server 2007 does not check the hosts file if the Edge Transport server has no DNS server configured.
To resolve this problem, install the following update rollup:
979784 Description of Update Rollup 3 for Exchange Server 2007 Service Pack 2
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
For more information about how to configure DNS settings for Exchange 2007 Servers, visit the following Microsoft Web site: