Beginning Monday, the US Postal Service is accepting letters for the 109-year-old USPS Operation Santa program. Letters must be postmarked by December 10 and will be uploaded online through December 15 for potential adoption. USPS Operation Santa was established by the USPS to help those in need during the holidays. The program is intended to help as many families as possible experience a happy holiday season. USPS said that can only happen if there are letters to post on USPSOperationSanta.