All depends on _how_ it's sent. If it's an envelope, even a larger one, it's one thing. If it's a padded envelope or a "thick" envelope, it's another. Weight isn't the only factor. I can send a flat rate Priority Mail box that has nothing inside and weighs less than an 8x10 envelope with a piece of cardboard as stiffner, and yet, because it's a flat rate Priority Mail box, it'll cost more than the envelope - even if the envelope weighs more.

Thanks for the response. That seems very weird to me.... particularly because as I said I have sent larger envelopes that weigh more and have cost 2 international reply coupons to return

If my assumption is that it's being sent from the US to you is correct, it's this: A piece of cardboard to keep it from bending *may* cause it to be sent not as a letter but as a package, which is a higher cost than sending a letter. Depends on the thickness of the cardboard. Some clerks *may* ignore/not notice/not care about the cardboard and send it as a letter, but the majority of clerks, feeling the thickness and/or the "DO NOT BEND" markings "have" to send it as a package.

Hi there

USPS is ignoring my queries ( they have seen my messages on social media ) I can't ring because I live overseas.

I sent a parcel to request an autograph for a friend and provided 3 international reply coupons for return. The item in question is a DVD cover just the cover and a small piece of cardboard to stop it from bending. The return envelope is a 210 x 274mm padded bag. The office that's going to return the parcel to me said usps said they couldn't send it as a letter and as a result 3 reply coupons aren't enough and it will cost an additional 12 usd. This has left me very confused as I have sent 8x10 photo's in much larger envelopes and 2 international reply coupons have been enough for postage.
I'm honestly shocked the clerk at usps has said this. Can anyone hazard a guess as to what's going on?

I have never had this issue before.

Thanks for your time.