JF Ptak Science Books Quick Post
This seems as though it was an interesting idea back in 1934–but no doubt there were others thinking that instead of dropping mail on a city by a rocket that another payload could be substituted…better yet, just use the entire rocket for this delivery-of-something-else item and dispense with the parachute altogether. In any event, the idea never caught on (though megastars of rocket flight Hermann Oberth and Eugene Sanger discussed its possibilities in a positive light), and it seems as though there was only one instance of USPS rocket mail delivery–a converted nuclear-warheadless SSM-N-8 cruise missile was used to do so in 1959, and that seems about it.
{Source: Popular Mechanics, April 1934]