451 4.4 dns query failed on exchange 2010 hub transport server

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We have configured exchange 2010 hub transport server on our internal network.

We also have exchange 2010 edge transport server in DMZ.

We cannot send emails to external domains.

The error what we get on hub transport server is

" 451 4.4.0 DNS query failed. SMTPSEND.DNS

The mail does not even go to edge transport server as we cant see any queue on our edge transport server.

1) use nslookup test is ok, can resolve MX record.
2) telnet 25 port and ping edge server no problem.
3) ping hub server form edge server is ok.
4) send connector synchronization is ok.

How do we resolve this issue?

leo chui


I would like to suggest you create a edge subscription file and import it on the hub transfer server role.

To create : New-EdgeSubscription -FileName " C:\EdgeSubscriptionInfo.xml"

To import the file:
In the console tree, navigate to Organization Configuration > Hub Transport. In the result pane, click the Edge Subscriptions tab. In the action pane, click New Edge Subscription. On the New Edge Subscription page, complete the following fields: Active Directory site Click Browse, and then select an Active Directory site in the drop-down list. This field identifies the Active Directory site where the Hub Transport server is connecting to the Edge Transport server for which the Edge Subscription exists. Subscription file Click Browse, and then select an Edge Subscription file. Automatically create a Send connector for this Edge Subscription Select this check box to automatically create a Send connector that routes messages from the Exchange organization to the Internet. The Edge Subscription is configured as the source server for the Send connector. The Send connector is configured to route messages to all domains by using Domain Name System (DNS) MX resource records. Click New to create the new Edge Subscription. On the Completion page, review the following, and then click Finish to close the wizard: A status of Completed indicates that the wizard completed the task successfully. A status of Failed indicates that the task wasn't completed. If the task fails, review the summary for an explanation, and then click Back to make any configuration changes.

Detail refer to :

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