Have you experienced recieving a mail without anything in it? For the first time, I did. Though the USPS put the original envelope in another envelope, the original mail is obviously empty as it was damaged. Look what happened to the envelope at the lower part area.
At the back of the USPS envelope, USPS explained that due to high volume of mail they handle everyday and though they handle everything with care, there are times that some mails get damaged. I never attempted to open the USPS envelope just in case I have to return the original mail to the sender.