[Today’s post comes to us courtesy of Ping Xu]

Symptoms:

Replacing a network adapter on the Essential Business Server 2008 Security Server may cause inbound and outbound email to queue and not be delivered. Confirm this by checking the message queue on the Security Server:

1. Start the Exchange Management Console on the Security Server.
2. Click Toolbox.
3. Select Queue Viewer under the Mail flow tools category to open the Queue Viewer tool.
4. Review the information in the Last Error column. Note whether you have an inbound/outbound message queue and if there is an error similar to "451 4.4.0 DNS Query Failed".

Resolution:

Reconfigure Internal and External DNS Lookups settings by using the Exchange Management Console.

Reconfigure Internal DNS Lookups setting:

1. Log on locally to the Security Server.
2. Open the Exchange Management Console.
3. Select the Edge Transport server in the Result pane, and then select Properties.
4. Select the Internal DNS Lookups tab.
5. Select your internal Network Adapter in Use network card DNS settings drop down list and click OK.

Reconfigure External DNS Lookups setting:

1. Log on locally to the Security Server.
2. Open the Exchange Management Console.
3. Select the Edge Transport server in the Result pane, and select Properties.
4. Select the External DNS Lookups tab.
5. Select your External Network Adapter in Use network card DNS settings drop down list and click OK.

Reference:

http://technet.microsoft.com/en-us/library/bb851512.aspx