CLEVELAND, Ohio - December is here, and that means knowing when to mail and - most importantly - when not to. There are many mailing options, from the U.S. Postal Service to private companies. Like Santa and his elves, workers at USPS and other services are on tight deadlines at their busiest time of the year. We checked with USPS, UPS and Amazon. Here are dates and tips to know: Ship First Class mail - including cards - via U.S. Postal Service by Tuesday, Dec. 19 to arrive before Christmas. Bill Sikes, Associated Press  KEY DATES Thursday, Dec. 7: U.S. Postal Service First Class International Service to Europe for Christmas delivery. Monday, Dec. 11: For arrival by Christmas, most of the military (APO/FPO/DPO) deadlines are on this date for Priority Mail and First Class. Here's the full deadline schedule. Tuesday, Dec. 12: Hanukkah starts. David Van Allen, who coordinates USPS Strategic Communications for the Northern Ohio and Ohio Valley districts, suggests mailing about five days prior for gifts to arrive in time. "Earlier is way better," he said. (Hanukkah runs until Wednesday, Dec. 20.) Thursday, Dec. 14: USPS retail ground-shipping deadline for arrival in time for Christmas. Friday, Dec. 15: Order by this date for free shipping via Amazon for Christmas delivery. Also, "Letters from Santa" must be received by the Anchorage, Alaska, postmaster by this date. USPS suggests using #LettersFromSanta on social media when your child receives the response. (See below for details.) Saturday, Dec. 16: Most of the military (APO/FPO/DPO) deadlines for Priority Mail Express fall on this date for Christmas delivery. Monday, Dec. 18 - Saturday, Dec. 24: This is the week to avoid. It's the Postal Service's busiest mailing, shipping and delivery week. USPS expects to handle almost 3 billion pieces of First Class Mail. (The Post Office no longer declares one specific date as "busiest mailing day of the year." "It's more of a busiest mailing week," Van Allen said. "Because of online mailing and packages, it got kind of shifted." Monday, Dec. 18: U.S. Postal Service's anticipated busiest day online with more than 7 million people hitting Also, order by this date for