Exchange Online transport rules can block outbound email stamped with selected Office 365 Sensitivity Labels to make sure that confidential material doesn’t leave organizations. The transport rule is very easy to construct with the only complication being the need to discover the GUID of the sensitivity label you want to block. Fortunately, PowerShell gives us an easy way to find a label’s GUID.
https://office365itpros.com/2019/12/16/blocking-outbound-messages-stamped-office-365-sensitivity-lab...
