Payton screwed up. Should've gotten a Lawyer.

Prove that he read it before that day.

again, you can't. You actually can't prove anything which is why payton should've just kept his mouth shut.

You're right. I'm sure Sean Payton never read that email. And I'm sure he magically filtered his email to preclude any messages that mentioned things like "bounties", "hurting players for cash", etc....even though he had no knowledge this was going on in the locker room.