I always thought that the only envelopes the PO could crush were First Class Letters (thinner than 1/4"). Those go through the high-speed rollers and usually get crushed.
Then a postal clerk warned me that paying for "hand-stamp" or "manual processing" means nothing to the jerks that feed the sortation machines.
"If they can force them in, they might do that because it's easier for THEM, even if it causes jams that destroy many letters."
So now I beware ever sending a "skinny" bubble mailer. If it is much thinner than a full inch, I add padding until NO ONE could even TRY to force it into the crusher-rollers, no matter how "Postal" they have gone.
Same with the Flat Rate Envelopes. Since they have no weight limits, I have even put my seeds into bubble mailers INSIDE the big flat-rate envelope, to make sure that they get hand-cancelled or at least never go through First Class Letter pinch rollers.
