Receiving surprise letters, greeting cards, packages and gifts in the mail—and not just advertisements and bills—remains one of life’s simple pleasures. Even with the introduction of email and text messaging, the Postal Service continues its mission to deliver. All the while, it’s remained an integral part of American culture.

The U.S. Postal Service is celebrating its 250th anniversary this weekend, and you won't have to check your mailbox for the invite. The agency's semiquincentennial will be marked by an event at the Smithsonian's National Postal Museum in Washington,