Postmarked mail is mail that has a postal marking made on it, indicating the place, date, and time that the item was delivered into the care of a postal service. Postmarks are imprints on letters, flats, and parcels that show the name of the United States Postal Service (USPS) office that accepted custody of the mail, along with the state, zip code, and the date of mailing. The postmark is generally applied, either by machine or by hand, with cancellation bars to indicate that the postage cannot be reused. Postmarks are important for determining the date that a piece of mail was sent, which can be used to determine if a payment was mailed on or before the tax deadline. It is important to note that the USPS only postmarks certain mail depending on the type of postage used, and may not postmark mail on the same day deposited into a receptacle.