Exchange 2016 Mailbox Server cannot send mail to another 2016 Mailbox Server

RAJEEV GUJRAL 96 Reputation points

I recently upgraded one of the Exchange Mailbox 2016 Servers with CU19 while the other one is still running on CU11. After upgrading the second mailbox server to CU19, first mailbox server (CU11) can't send mails to another mailbox server (CU19) and vice-versa. Getting "Exchange Auth Failure". When checked logs, getting "target machine actively refused the connection". Default receive connector is having "Exch. Server Auth." enabled. I am even able to TELNET both the mailbox servers from each other. No SMTP inspection enables on firewalls. Any ideas please?

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.
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  1. RAJEEV GUJRAL 96 Reputation points

    Hi @Lucas Liu-MSFT ,
    Resolved the issue.
    Got an alert in Event Viewer regarding the SMTP certificate binding and missing entry in ROUTING GROUP MEMBER in Active Directory.
    Edited the Active Driectroy (ADSIEdit) and added the second MBX server in the routinggroupmembers attribute. Also, removed the certificate and re-installed and inter-mailbox server traffic was up and running.

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  1. Lucas Liu-MSFT 6,161 Reputation points

    Are the two Exchange servers in the same domain?
    Can mailbox in these two Exchange servers send mail to external recipients or receive mail from external senders?
    Are there any non-delivery reports generated when the email fails to be sent? If so, please share the complete report with us, please noted that covering your personal information.

    Microsoft does not recommend deploying any firewall or network equipment between internal Exchange servers. Please make sure that all communications and traffic between your internal Exchange servers are not restricted, and make sure that you open all ports required by Exchange. In addition, if possible, please try to temporarily turn off the firewall to check whether the mail can be sent successfully.
    For more information you could refer to: Network ports for clients and mail flow in Exchange

    The following screenshot is the defaul settings of Default receive connector in exchange server, you can compare with the receive connector in your environment.


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