According to the search results, USPS delivers mail from Monday to Saturday in ordinary circumstances. However, the delivery time and hours depend on the location of the USPS warehouse and the place where they store your mail and packages before delivering them to your assigned address. Priority Mail & Priority Mail Express items might be delivered on Saturdays. USPS does not deliver mail on Sundays throughout the year. USPS also does not operate on federal holidays, such as Christmas Day and Thanksgiving Day. However, USPS delivers Amazon Packages and Priority Mail Packages on Sundays. The delivery time for Sunday varies, but if you choose Priority Mail Express, your shipments should arrive by 10:30 am.