We are seeing the following from the connectivity tester:
Testing inbound SMTP mail flow for domain 'email@example.com'.
The Microsoft Connectivity Analyzer failed to test inbound SMTP mail flow.
Attempting to retrieve DNS MX records for domain 'domain.suffix'.
One or more MX records were successfully retrieved from DNS.
Testing Mail Exchanger myemail.domain.suffix.
One or more SMTP tests failed for this Mail Exchanger.
Attempting to resolve the host name myemail.domain.suffix in DNS.
The host name resolved successfully.
Testing TCP port 25 on host myemail.domain.suffix to ensure it's listening and open.
The port was opened successfully.
Analyzing SMTP Capabilities for server myemail.domain.suffix:25
SMTP Capabilities were analyzed successfuly.
Attempting to send a test email message to firstname.lastname@example.org using MX myemail.domain.suffix.
Delivery of the test email message failed.
The server returned status code 451 - Error in processing. The server response was: 4.7.0 Temporary server error. Please try again later. PRX4
Message: Error in processing. The server response was: 4.7.0 Temporary server error. Please try again later. PRX4
at System.Net.Mail.DataStopCommand.CheckResponse(SmtpStatusCode statusCode, String serverResponse)
at System.Net.Mail.DataStopCommand.Send(SmtpConnection conn)
at System.Net.Mail.SmtpClient.Send(MailMessage message)
Elapsed Time: 11387 ms.
We have manually changed the DNS on both the server OS and the Exchange ECP but nothing seems to work.