The word 'etiquette' reminds me of vicarage ladies discussing which way their pinkies ought to point when holding a tea-cup, but I use the word here with respect to the problem of friends who don't, can't or won't, respond.
I don't email much, and typically my 'you have mail' box may have anything between zero and three new emails each morning. I know people who apparently receive as many as 80 a day, excluding advertising! (How such a phenomenon occurs I'm not sure. They must be very talkative.)
There are at least two famous airlifts associated with World War II. In 1942, when the last route from India to China was cut off, FDR made the decision that it was imperative China receive armaments and supplies for the Army Air Force in China, which was struggling to pin down Japanese forces. Both the US and UK began the appallingly dangerous air lift over the Himalayas -- from Assam (famous for its tea) in India to Kunming in China.