The U.S. Postal Service is expecting its busiest day of the year today, kicking off the second half of the holiday season that began the day after Thanksgiving and runs through New Year’s Day.

Nationwide, the postal service is expecting to see more than 19 billion letters, holiday cards and packages go through its system this year. Just today, postal officials expect nearly 280 million cards and letters.

Michael Miles, a communication manager for the postal system, said packages to be delivered by Christmas Day will need to be at the post office no later than Dec. 20.