In 1934-1936 the German Gerhard Zucker tried to convince the General Post Office that postal delivery by rocket was viable and carried out several experiments. Although initial tests were a success, rockets on longer flights exploded before reaching their intended destinations and as such it has never been seen as a feasible way of delivering the post.
1900s Airmail numbers
1700s Improving the speed and efficiency of mail delivery
1800s Mail deliveries in all weather – Samuel Henry Alken oil painting
1800s Escaped lioness attacks mail in Salisbury! (1817)
1700s John Pratt writes to John Palmer to inform him that he hasn’t been appointed to Government (August 1782), (from the private papers of John Palmer)
1900s Mobile post office and tractor (trailer: 1937, tractor: 1954)