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Exchange 2013 SMTP receive connector error 554 5.4.4

Last Updated: 8/1/17


emails are not received or are received with a delay. sending mail server received error: 451 4.7.0 Temporary server error. Please try again later. PRX2 (Reason:451 4.7.0 Temporary server error. Please try again later. PRX2 )

Error message from Exchange 2013 logs: Message or connection acked with status Fail and response 554 5.4.4 SMTPSEND.DNS.NonExistentDomain; nonexistent domain.
(Log file location: c:\Program Files\Microsoft\Exchange Server\V15\TransportRoles\Logs\FrontEnd\ProtocolLog\SmtpReceive)



This started happening on the same day the we implemented split DNS (seperate external and internal DNS records). Since we were significantly reducing which internal records were made available externally; I believe that this is what caused the problem. Normally this would not cause an issue except that we had both external (read: public) and internal DNS servers on the exchange server NIC.


remove external DNS servers from exchange server NIC and flush your DNS cache.
Note: we are still in the middle of this, so this solution is not fully confirmed.

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