They take pictures of the letters as they come in from all angles, and then a computer algorithm builds a 3D structure of the letter so they know how big it is and which machines it can and can’t go through if it’s too big to go through a particular machine it gets redirected to another process. Also they have metal detectors so the keys would be detected right away.

Maybe in the '90s this was a problem with large items in envelopes but not anymore because they can detect it before it gets anywhere near the problem machine.

They have a whole list of things you can and can’t post and one of the things you can post is live insects so obviously they’re not mangling everything to an auto sorter.