While the United States Postal Service (USPS) operates every day of the year, including Christmas Day, delivery on this holiday is limited to Priority Mail Express and Amazon packages. This means that most regular mail and packages will not be delivered on Christmas Day. However, if you need to send a gift or card on Christmas Day, you can use Priority Mail Express, which offers guaranteed overnight delivery. The cost for this service is higher than regular mail or packages, but it is a great option if you need to ensure that your item arrives on Christmas Day.