Exchange Server 2016: Test Mail Flow from PowerShell.
The Test-Mailflow cmdlet can be used to diagnose whether mail can be successfully sent and delivered.
To send a test probe message to the administrator's email address, use the following command:
Test-Mailflow -TargetEmailAddress administrator@mstechguru.ae
Exchange Management Shell:
Here are the results:-
This may help you to do the testing from PowerShell and troubleshoot the mail flow related issues.