Unable to send emails from OnPrem Exchange 2019 to external domains in Hybrid Setup

Imran Syed 0

We are Using a wildcard certificate (*.domain.com)

Unable to send emails from OnPrem Exchange 2019 to external domains in Hybrid Setup.

Verified certificate thumbprint on send connector, receive connectors and transport service.

Below is the error:

Outbound TLS authentication failed with error SubjectMismatch for Send connector Outbound to Office 365 - 84a08efe-69a3-4c36-8830-6673b4fab3a7. The TLS authentication mechanism is DomainValidation. Target is gmail.com.

Please advise.

Aholic Liang-MSFT 13,846 Reputation points Microsoft Vendor

2023-09-12T02:13:55.53+00:00

Hi @Imran Syed,

if you find the reply above helpful, do you mind accepting it as answer to help increase visibility of this question for other members of the Microsoft Q&A community? If you still have further concerns about this thread, feel free to post back.

1 answer

Andy David - MVP 147.6K Reputation points MVP

2023-09-06T16:50:34.61+00:00
Make sure there are no network devices between your on-prem org and Exchange Online that may be interfering

Is the inbound hybrid connector on the Exchange Online configured with the domain set on the cert?

https://learn.microsoft.com/en-us/exchange/certificate-requirements
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Unable to send emails from OnPrem Exchange 2019 to external domains in Hybrid Setup

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