I'm the last person to complain about the USPS, but this has got to be one for the books...!

My local post office told me these envelopes can not be accepted... I was once told this about 15-years ago as well, but still used them w/o any problem...

They're the same size as #10 envelopes... and I've used two different types in the past; this, and one that's printed w/ a "Via Air Mail/Correo Aereo/Par Avion" just under where stamp should be affixed.

I asked why, but only told they're not accepted... I asked if it's because they're lightweight, but just got a shoulder shrug... (?)

Maybe it's a scanning issue, but I can't see how with the way some of these return envelopes are decorated with advertising... (?)