|Mailmen are real mavericks.|
When someone “Pushes the envelope” it means they’re testing the limits of what’s possible. That means people who work for the US Postal Service are the most extreme people alive. Mail carriers push the envelope on a constant basis. They don’t push it too far though, just far enough into the mailbox to close it. Mail sorters don’t just push the envelope, they push thousands of envelopes daily, sometimes they might even toss a few which is far more extreme than just pushing.
If you’ve ever literally pushed an envelope before you know it’s perhaps the farthest thing you can get from figuratively pushing an envelope. There is the possibility this saying refers to the “flight envelope” which is the limit to which a plane can be flown safely. However, when people hear the phrase “push the envelope” 9 out of 10 are thinking about paper letter travel clothing, not aerodynamic physics. This saying is totally lost on modern day people so it’s obsolete and therefore “dumbass” even though in this case the people are probably more to blame.