USPS Says Guaranteed Overnight Isn't Guaranteed. What?

USPS Says Guaranteed Overnight Isn't Guaranteed. What?

Dorothy found out that the USPS’s guaranteed overnight delivery doesn’t apply if you use their Express Mail boxes, because “Letters get stuck up in the top of the box all the time. Sometimes, it takes days or even a week before we find them.” Hey post office, maybe you should try to check the top of the box every day. Problem solved!