USPS delivers on Sunday ahead of holiday week

 USPS is projecting it will deliver more than 15.5 billion pieces of mail for the 2015 holiday season.

Mail carriers are even working on Sundays leading up to the holidays to make sure all of the mail sent makes it on time.

The post off says it's expecting more than 30 million packages will be delivered on Monday December 21st alone, marking the busiest delivery day of the year.