When an event has played out, it is often hard to see how it could have happened any other way. The first airplanes flew, but the limitations of early technology made them cumbersome affairs. Wing design was primitive, providing minimal lift. Materials that made up the plane were heavy compared to the structure they provided, and engines were weighty, generating far less power per pound of metal than do modern engines. All of this meant that though the early airplanes flew, they could carry little more than the pilot. Range of flight was short, not so much because of the probability of engine trouble, but because fuel was heavy, and there was a point at which carrying enough to fly a long distance meant that the plane was too heavy to achieve lift. There was no room on these early airplanes for mail, except for a few philatelic pieces that were carried as favors, or promotional items, or at very high postage prices.
Zeppelins had far fewer weight restrictions. Lighter than air ships, Zeppelins used the nature of the gases that they were filled with to achieve lift, using relatively small engines for motion. Though Zeppelins were used in WWI for military matters, including bombing runs, it was in the 1920s that they began to be developed for passenger travel and freight, including mail. By 1928, Zeppelins were beginning flights across the Atlantic delivering tons of passengers and post, rather than the few scrawny letters that went with Lindbergh in his first airplane transatlantic crossing in 1927. If we were looking at the future of transportation from the vantage point of 1930, it would have been hard to imagine that zeppelins would disappear and that huge airplanes would carry airmail in such quantities that for most airmail services there is no surcharge over ordinary first class rates.
Postal Agencies responded with special stamps for zeppelin mail service. Nearly twenty countries issued these special stamps, though zeppelin mail was very expensive and continued to be more of a curiosity than a service used by businesses. The conclusion of the story is that converging technologies intersected to change how mail was sent. Wing and engine design allowed planes to fly longer routes with greater payloads and shortages of helium led to hydrogen use in zeppelins leading to the Hindenburg disaster in 1937. After that zeppelins were done. Zeppelin stamps, though, have continued to be an important part of philately and figure as some of the most sought out stamps in many of the countries that issued them. Over the last twenty-five years though the popularity of zeppelins has declined. This is due to the phenomenon that collectors, as adults, tend to most desire the stamps of their youth that they aspired to and couldn't afford. As the Greatest Generation has aged out of the philatelic market, the collectors exerting market pressure today are no longer familiar with the wonderful story of early air flight.