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

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