LOS ANGELES (CBSLA.com) — Monday, Dec. 17 is the busiest shipping and mailing day of the year, according to the United States Postal Service.

Americans will send more than 658 million pieces of mail with the USPS on Dec. 17, an increase of 20 percent over 2011.

“The most important thing is to make sure they’ve got the correct and complete address. Don’t forget those directionals, the apartment number, suite numbers and make sure the zip code is correct,” Richard Maher of the USPS said.

Recommended mail-by dates for Christmas delivery:

Dec. 20 – First-Class Mail
Dec. 21 – Priority Mail
Dec. 22 – Express Mail

The Postal Service projects it will deliver about 18 billion cards, letters and packages between Thanksgiving and Christmas Eve. Included in that number is 365 million packages, officials said.