Can't receive mail in a hybrid environment after you install a new certificate on the server

Original KB number:   2989382


After you install a new Exchange certificate in an Exchange Server hybrid environment, you experience the following symptoms:

  • You cannot receive mail from the Internet or from Microsoft 365 when you use Transport Layer Security (TLS).

  • If you use Telnet (for example, telnet localhost 25) to examine Simple Mail Transfer Protocol (SMTP) communications, you notice that the STARTTLS command is missing.

  • If you examine the Application log in Event Viewer, you see an event entry that resembles the following:

    Log Name: Application
    Source: MSExchangeFrontEndTransport
    Date: MM/DD/YYYY 0:00:00 AM
    Event ID: 12014
    Task Category: TransportService
    Level: Error
    Keywords: Classic
    User: N/A
    Computer: <HybridServerName>
    Microsoft Exchange could not find a certificate that contains the domain name <I>CN=Certificate Name, OU=<CertificateIssuer>, O=Certificate Provider, C=US<S>, OU=IT, O=contoso, L=location, S=location, C=US in the personal store on the local computer.

  • The check connectivity test to the on-premises server fails, and you receive the following error message:

    450 4.4.101 Proxy session setup failed on Frontend with '451 4.4.0 Primary target IP address responded with "451 5.7.3 STARTTLS is required to send mail." Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts. The last endpoint attempted was <endpoint>'.


This issue occurs if the TlsCertificateName property of the hybrid server's receive connector contains incorrect certificate information after a new Exchange certificate is installed and old certificate that is used for hybrid mail flow is removed.

The TlsCertificateName property is set correctly when the Hybrid Configuration wizard (HCW) is run after a new Exchange certificate is installed.

However, if the HCW is not run, or if a failure occurs for any other reason when you run the HCW, the TlsCertificateName property is not updated, and the new Exchange certificate is not used by the hybrid server's receive connector.

In this scenario, the STARTTLS command is not present in SMTP communications, and the mail flow from Microsoft 365 fails.


Make sure that the new certificate is enabled for SMTP. If it's not, run the following command to enable the SMTP service on the newly installed certificate.

Enable-ExchangeCertificate <thumbprint> -services SMTP


Select No when you are prompted to overwrite the default certificate). Otherwise, EdgeSync breaks and has to be re-created. Then, remove the TlsCertificateName property from the receive connector on the hybrid server. To do this, run the following command:

Get-ReceiveConnector "ServerName\Default Frontend ReceiveConnector" | Set-ReceiveConnector -TlsCertificateName $null

Rerun the Hybrid Configuration wizard to update the receive connector on the hybrid server that has the newly installed certificate information.

More information

For more information, see Certificate requirements for hybrid deployments.

Still need help? Go to Microsoft Community or the Exchange TechNet Forums.