Mail Quotes
Slightly adapted, this passage became the slogan of the U. S. Postal Service:
Lewis is referring to his time spent as an Intelligence Officer in Naples, Italy.
There was no probable cause required at the time and the military intelligence people routinely opened all mail and read it. Most people did not object as the intensity of winning World War II so great that most people put up with almost anything provided it was done in good faith to further the war effort.