It always amazes me to see what the USPS will attempt to stuff into our mailbox, damaging the box in the process.

And anytime a company puts "Do Not Bend" on the envelope or package, I think they read it as, "Not only bend this, see if you can fold a crease in it!" I have a reasonably sized mailbox, and the guy would still fold (with a crease) my Spiderman comics that included a piece of cardboard (and the "Do Not Bend" label).

If it's important, I always double box the item, put strong enough cardboard in the envelope that keeps it from being bent, etc.