I was surprised a few years ago to find that a similar thing was already happening for big company email servers. My small company was working a joint proposal

I was surprised a few years ago to find that a similar thing was already happening for big company email servers. My small company was working a joint proposal with a division of a big company. Every time the teammate at BigCo sent me his copy of the Word document containing the proposal, it would mysteriously disappear en route through his Exchange server. Once he removed the "Confidential Property of BigCo" footer from the document it went through just fine. He was hitherto unaware that such a restriction existed. It was a violation of his company's policy that he send a document with that footer outside of his network. It was also a violation of policy for him to remove that footer from a proposal for which his company would be the prime contractor. There's a lesson in there somewhere about centralized automatic enforcement of policy.