I can't find an option for large envelope on PayPal. I always choose First Class Parcel (2-5 days) - Package/Thick envelope. It's the delivery confirmation that's included that caused it to be not delivered. The USPS regulation is "All items (except Priority Mail) mailed with Delivery Confirmation must measure at least 3/4" at the thickest point, or be in a rigid box."

Technically I was wrong but I'm still pissed. There's no telling how many thousands of #000 packages are mailed daily using the same options from PayPal postage. I got 4 in the mail today with the same options that I used, no problem, they were in the mailbox waiting when I got home. The whole thing just doesn't make a lot of sense to me... a nice compact, flat mailer, easy for the postman to handle, easy to transport vs a small mailer with a 3/4" bulge in the middle. There's no difference in the postage amount by putting a couple of styrofoam peanuts in the mailer to make it 3/4" so what do they gain.