“Mail hacking” was a thing. I forget the name they gave it but read an article in 2600 or Phrack some time ago that talked about some of the tricks like the one

“Mail hacking” was a thing. I forget the name they gave it but read an article in 2600 or Phrack some time ago that talked about some of the tricks like the one you mentioned. The only other one I remember was to put a smear of Vaseline in the corner where stamps normally go. It was enough to trick the sorting machine.