German censor cachet
Mersch, April 10, 1940, to Neurath [post: Neuerburg], Germany
The Reich officially established its mail surveillance system by directive issued on April 2, 1940 and published on June 8, 1940. As a consequence, incoming mail to the Reich from Luxembourg was already subject to censorship when the Grand Duchy was occupied on May 10, 1940. Here is an example of such censorship during the twenty-day period between April 2nd and May10th.
Some writers state that German censorship began even earlier. What is the earliest date that incoming mail to the Reich from Luxembourg was censored?