Fix: Exhcange 2010 Error 451 4.4.0 Error DNS Query Failed

There seem to be an issue with Windows SBS Small Business Server 2011 or Windows Server 2008/ R2 running both Exchange 2010 SP1 Rollup 3 or 4. This has happened many times and gone through the Exchange and router configuration many times with no success. Here is the simple workaround to this teething issue. The issue seems to be a bug from Microsoft where if you have IPV4 along with IPV6 enabled. The IPV6 will be used to resolve the DNS when sending an email. This will fail and the user will either get a delivery report or a delay report.

To solve the issue, simple do the following:

– Open the ‘Exchange Management Console’
– Expand the ‘Server Configuration’ node
– Right Click and select ‘Properties’ on teh server in the content window (This will popup the server’s property window)
– Click on the ‘External DNS Lookups’
– Select ‘Use These DNS Servers’ radio button and add the external DNS IP addresses of your ISP
– Click on the ‘OK’ button to save the configuration
– Expand the ‘Organization Configuration’ node and click on the ‘Send Connectors’ tab
– Right click on your send connector and select ‘Properties’
– Click on the ‘Network’ tab
– Tick the option to ‘Use domain name system (DNS) MX records to route mail automatically’ and make sure to tick the ‘Use the External DNS Lookup settings on the transport server

This should solve the problem and it will process all the mail in the queue of Exchange. Of course depending if you have the right configuration and ports open from the router.

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