To ensure holiday delivery of cards, letters and packages in the United States by Dec. 25, the U.S. Postal Service recommends customers ship items by the following dates:
Dec. 15 -- Standard post, ground service for less-than-urgent deliveries and oversized packages
Dec. 19 -- First class, for standard-size envelopes and small packages weighing up to 13 ounces with delivery in three or fewer business days
Dec. 21 -- Priority Mail for delivery in one to three business days
Dec. 23 -- Priority Mail Express, with guaranteed overnight scheduled delivery to most locations
The deadline for international mail generally is Dec. 1. For packages to military members worldwide it's Nov. 25 for space-available mail and Dec. 3 or Dec. 10 for first-class letters and cards or Priority Mail.
A complete list of deadlines is available at usps.com.