Hi @RAJEEV GUJRAL ,
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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