When did the Penny Black become valid for postage in England?

The Penny Black, recognized as the world's first adhesive postage stamp, became valid for use in England on May 6, 1840. While the stamps were made available for purchase starting May 1, 1840, they were not officially permitted for postal use until the subsequent week.12

This historic issue sparked the enduring hobby of philately, as collectors began seeking out these early stamps almost immediately after their introduction.1