451 4.4.0 dns query failed

Recently I came across a sending error on a Microsoft Exchange 2016 server after having performed an update on the server and a reboot that followed. After the reboot everything seemed to be working fine. When I tried to send an e-mail and looked at the mailqueue on the server using the Queue Viewer (which can be found within the ‘Exchange Toolbox’) I noticed that e-mails to external domains were not send and were kept in a queue list to be retried with the following errorline:

451 4.4.0 dns query failed

This should be clear enough; the DNS could not resolve the MX record for the specified domain. But when using ‘nslookup’ the mx records for all the domains resolved fine. Looking further in the ‘Event viewer’ and specific the logbook for ‘Windows Logs’ > ‘Application’ I found events with ID 16025.

No DNS servers could be retrieved from network adapter {device-id}. Check if the computer is connected to a network and Get-NetworkConnectionInfo returns any result.

That’s weird, the nslookup could use the DNS server given by the network adapter, and only one network adapter is installed. So I went to the ECP (aka Exchange Admin Panel), selected the ‘servers’ menu-item and opened the settings for the server giving those issues. I went to ‘DNS lookups’ in the menu in the new screen that appeared and saw no addresses listed for the External DNS lookups even though the option ‘All network adapters (All available IPv4)’ was selected. So, because only one network adapter was installed, I chose to select the specific adapter to be used, clicked save and the DNS Servers were found. After retrying in the queue-list the mails were successfully send.

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