The Test-Message cmdlet is a useful tool to check if Exchange transport rules and DLP policies work correctly. You can input a test message to see what happens as the Exchange transport service applies transport rules, DLP policies, and auto-label policies based on the message contents and properties. Nice as it is to have the Test-Message cmdlet, human knowledge of what transport rules should do is probably an even more important asset.
https://office365itpros.com/2023/02/27/test-message-exchange-cmdlet/
