Gentlemen do not read each other's mail.
Henry L. Stimson, reported in Stimson and McGeorge Bundy, On Active Service in Peace and War (1948), p. 188; David Kahn, The Codebreakers (1967), p. 360. This was Stimson's justification for closing the Department of State's code-breaking office, the so-called Black Chamber, in 1929.