Martin Luther King Day is one of 10 official 2010 post office holidays, meaning mail will not be delivered today and post offices will be closed.
The United States Postal Service runs on the Federal Holiday schedule.
Here is the complete list of post office holidays 2010:
Friday, January 1 - New Year's Day
Monday, January 18 - Martin Luther King Jr's Birthday
Monday, February 15 - Washington's Birthday (President's Day)
Monday, May 31 - Memorial Day
Sunday, July 4 - Independence Day
Monday, September 6 - Labor Day
Monday, October 11 - Columbus Day
Wednesday, November 11 - Veterans Day
Thursday, November 25 - Thanksgiving Day
Saturday, December 25 - Christmas Day