What is recognized as the USPS's fastest mail service?

The fastest mail service offered by the USPS is Express Mail, known today as Priority Mail Express. This service guarantees overnight delivery to most U.S. addresses, ensuring that customers receive their mail quickly and reliably. Priority Mail Express also includes features such as tracking, signature confirmation, and insurance, which enhance its value and reliability as an expedited service.

While Priority Mail provides expedited delivery and typically reaches its destination within one to three business days, it does not guarantee overnight service in the same manner as Priority Mail Express. First-Class Mail provides swift delivery for letters and small packages but does not ensure specific delivery times. Lastly, Parcel Select is primarily an option for commercial customers for large and bulk shipments, and it does not prioritize speed like Express Mail does. Therefore, the unique characteristics and guarantees of Express Mail establish it as the USPS's fastest mail service.