This technique has been used for a while, and it's widely known. It's "easy" to defeat, you need to ask someone else for a copy, and match its contents/changes

This technique has been used for a while, and it's widely known. It's "easy" to defeat, you need to ask someone else for a copy, and match its contents/changes with the copy from the original leaker. I don't mean to say it's a bad idea, and it's standard practice in enterprise environments, but it's no silver bullet either. Plus, to align with parent messages, it won't prevent leaking, it just helps to identify the person.