Question: what is the difference between priority mail and overnight mail?
Answer: Our fastest domestic shipping service, Priority Mail Express® delivers 7 days a week, 365 days a year (with limited exceptions). Overnight delivery is available to most U.S. addresses and PO Boxes™2 with a money-back guarantee1. With our free Flat Rate Envelopes, you don't need to weigh shipments 70 lbs and under.