From 1908 until 1963, the collection was housed in the Smithsonian's Arts and Industries Building on the National Mall. In 1964, the collection was moved to the museum that is now known as the National Museum of American History. There, the collection expanded to include postal history and stamp production. The collection was then moved to its present location and the National Postal Museum opened on July 30, 1993.
In addition to one of the world's largest collections of stamps and philatelic materials, the National Postal Museum has postal history material that pre-dates stamps, vehicles used to transport the mail, mailboxes and mailbags, postal uniforms and equipment. -- from the website.