If the postal service invented physical systems that didn't allow mail to be opened in transit, would you accuse the postmaster general of facilitating criminal

If the postal service invented physical systems that didn't allow mail to be opened in transit, would you accuse the postmaster general of facilitating criminal conspiracies? All they are doing is keeping private communication really private. What is the difference between this and encrypted email? Hint, you can break a large file into many chunks of email too.