next day mail delivery is a shipping option that guarantees delivery of items by the next business day. USPS offers a service called Priority Mail Express that provides overnight delivery, with tracking and insurance included. Other carriers, such as FedEx and UPS, also offer similar services with their respective options for next-day deliveries. The cost for next-day mail delivery will vary based on the weight, dimensions, and destination of the package, with more urgent or distant deliveries typically costing more. This option is often used for time-sensitive documents and packages.