Postmark

A postmark, also known as a datestamp, is a marking on a piece of mail indicating the date and time it was received by a postal service. Beyond its functional role, the postmark has a rich history and continues to hold a special place in the world of philately.

In the legal world, the date on a postmark is king. The "Mailbox Rule" (common in contract law) states that a document is considered filed or accepted on the date it is , not the date the recipient receives it. If your tax return is due on April 15th, as long as the postmark on the envelope reads "April 15th" (or earlier), the IRS considers it on time—even if it arrives a week later. This single stamp prevents millions of dollars in late fees annually. postmark