Rocket mail is the delivery of mail by rocket or missile. (Something like a superfast snail mail.) The rocket would land by deploying an internal parachute upon arrival. It has been attempted by various organisations in many different countries, with varying levels of success. It has never been seen as being a viable option for delivering mail, due to the cost of the schemes and numerous failures.
The first Rocket Mail was launched in February 1931 by Friedrich Schmiedl (born in 1902), an engineer from Graz. He started a rocket with 100 letters aboard from Schoeckel hill to Sankt Radegund, a distance of two kilometres. But a few years later the property of explosive was avenged with death penalty. Schmiedl, an avowed pacifist, was afraid of using his documents for military research and burned them on the verge of the “occupation” by the Nazis.
After the war some research positions in the USA were offered, but Schmiedl cancelled (remember, he was pacifist) and became an official in the city council of Graz. He died in 1994.

(BTW: the English Wikipedia ^[1] about rocket mail doesn’t even mention Schmiedl’s name. But I’m too lazy to update it.)