Visit your local Post Office at 601 Tremont St! The Postal Service mission is to provide a reliable, efficient, trusted and affordable universal delivery service that connects people and helps businesses grow. The U.S. Postal Service is the only delivery service that reaches every address in the nation: 155 million residences, businesses and Post Office Boxes. With more than 31,600 retail locations and the most frequently visited website in the federal government, the Postal Service delivers 47 percent of the world’s mail.