Sending out Christmas greetings is a tradition that is still common today. Have you ever wondered just how many cards are sent across the country? According to Hallmark Corporate, 1.5 billion Christmas cards, including boxed and individual cards, are purchased and then sent every year in the U.S. This makes Christmas the No. 1 holiday for sending greetings, followed by Valentine's Day (144 million) and Mother's Day (133 million).