CHICAGO (CBS) — The U.S. Postal Service was preparing for what it expects to be the busiest mailing day of the year.

People were busy over the weekend, addressing envelopes and taping up boxes for cards and packages that will be sent out on Monday.

According to Postal Service spokeswoman Maureen Marion, more than 640 million pieces of mail will be dropped off at post offices, or put in mailboxes on Monday.

“On a typical Monday, the Postal Service will probably process in the vicinity of 500 to 520 million pieces of mail. We’re pretty busy on Mondays as is,” she said.

In the Chicago area alone, the Postal Service expects to handle more than 8.3 million cards, letters, and packages on Monday.

Anyone who wants to make sure a card or package makes it to its destination by Christmas, they should get it in the mail by Saturday.

The Postal Service said it is delivering seven days a week during the holidays in the Chicago area, including on Christmas Day.