'550 5.4.317 Message expired, cannot connect to remote server(SubjectMismatch)' Exchange Hybrid Error, Office 365 To On-prem User

Benard Mwanza 996 Reputation points
2021-12-09T04:30:05.307+00:00

Office 365 user cannot send email to exchange on-premise user. I get that error in NDR. '550 5.4.317 Message expired, cannot connect to remote server(SubjectMismatch)'

My AD connect server is health, its able to sync objects well

My exchange 2016 TLS 1.2, it has a valid SSL certificate bound both to receive and send connector.

Mails are able to flow from exchange server to office 365 hybrid. But not vice versa

That error occurs even when i try to validate the send connector from Office 365 to Exchange server. I deleted all my hybrid exchange connectors, rerun HCW two times, but still the same issue.

Exchange Server Management
Exchange Server Management
Exchange Server: A family of Microsoft client/server messaging and collaboration software.Management: The act or process of organizing, handling, directing or controlling something.
7,357 questions
Microsoft Exchange Hybrid Management
Microsoft Exchange Hybrid Management
Microsoft Exchange: Microsoft messaging and collaboration software.Hybrid Management: Organizing, handling, directing or controlling hybrid deployments.
1,896 questions
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Accepted answer
  1. Benard Mwanza 996 Reputation points
    2021-12-09T11:57:32.703+00:00

    I managed to resolve this issue. The problem was my internal mail gateway that receives external all inbound emails is using non-internet routable domain that does not resolve in the internet.

    After creating a new hybrid SSL certificate that i added the FQDN of that gateway, office 365 users were able to send to on-premises users without issues.

    2 people found this answer helpful.

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