1940's Formula Envelope/Cover From KZ Auschwitz

1940's formula envelope from Auschwitz concentration camp. Envelope has instructions to the sender and room for a signiture, name, birthdate, prisoner number and block. KL Auschwitz was the largest and most notorious of the Nazi concentration camps and extermination centers. Over 1.1 million men, women and children lost their lives there. Overall very fine condition. Second photo is a Google translation of the camp rules for mail.