December 20 is the prime mailing day for shoppers scrambling to send holiday gifts and cards in time for Christmas.
December 19 is also a big day for the postal service, with millions of packages delivered.
The postal service expects to deliver more than 16 billion letters packages and cards between Thanksgiving and New Year's Eve.
The Post Office recommends sending first class mail by December 20th, priority mail by the 21st, and then express mail by December 22nd.
