Today is the busiest day of the year for USPS

December 20, 2010 6:11:43 AM PST
Today is the busiest mail day of the year for the U.S Postal Service.

More than 800 million pieces of mail are expected to enter the system Monday. Today is the recommended deadline for sending greeting cards and holiday letters to make sure they arrive by Christmas.

Four San Francisco post offices even offered Sunday hours to help beat Monday's rush. Wednesday is the busiest delivery day for postal workers.