postal service overnight refers to a fast shipping service that guarantees delivery of mail and packages the next day, offered by postal services like USPS. When users search for “postal service overnight,” they are looking for options that allow them to send urgent items that must arrive by the next business day. USPS offers an overnight service known as Priority Mail Express, which guarantees next-day delivery to most U.S. addresses. The cost of overnight postal service depends on the weight, size, and destination of the item, with a flat-rate envelope option for certain shipments. Overnight services from other postal services, like FedEx and UPS, also provide similar fast delivery options. Choosing a postal service for overnight delivery requires understanding the specific needs of the shipment, whether it’s a letter, package, or document, and selecting the right carrier based on cost and delivery speed.