Goddammit Loch Ness Monster!

It just sounds like slavery with extra steps.

If you think about it from a security perspective, it makes sense. If a random person you don’t know sends you an email, the chances are non-zero that it contains something malicious. The provider has an obligation to filter emails that could be dangerous. They know that if a large email service sends an email, they have that same obligation and are therefore doing some filtering on their side to prevent malicious content. Trust is pretty important.