In England the Royal Mail delivers the post. In the United States the Postal Service delivers the mail. That's just one of hundreds, probably thousands, of examples of how Americans speak the same language as their cousins across the sea, but speak it very differently. Americans, of course, think the Brits talk funny, while the British think it is the Yanks who talk funny.
Books, movies, television, music and, of course, travel help Brits and Yanks understand one another, but the English spoken on opposite sides of the Atlantic Ocean remain very different.