The mythical father of Christmas doesn't actually have a house or mailbox, but you can address Santa mail to Santa Claus, North Pole, or any similar variation. The United States Postal Service accepts Santa letters through its Letters to Santa program.
The USPS has intercepted mail through its Letters for Santa program since 1912. Any mail addressed to Santa at the North Pole without a valid street address is collected and sent to the nearest participating post office location in the area of the letter's origin. Individuals can adopt redacted versions of these letters, purchase gifts on the child's list and return the gifts and letters to the post office for delivery to the letter writer.
Children can also send Santa letters to the town of North Pole, Alaska. Without a proper street address, the letters are held at the local post office. Letters can be received at Santa Claus House, 101 St. Nicholas Dr., North Pole, AK 99705. This business receives thousands of children's letters each year. Parents can arrange to have a letter from Santa mailed back to the child for a fee. This service has been offered for more than 60 years and includes a wide range of letter style and language options.
Another option is to send mail to Santa's Workshop at North Pole, New York, a Christmas and Santa themed workshop that opened in the 1950s. The mailing address is 324 Whiteface Memorial Highway, Wilmington, NY 12997.