I recently bought this SS envelope with letter. Not very important or valuable in itīs own right but I am genereting an interest in how to obtain more info from the markings on the envelope. Is there any books on the subject that you could recommend? Anything anyone can tell me about this one. Was the sender in an SS-Totenkopf artillerie rgt Situated in Dax France as the seller stated and how does this show up on the envelope? All help welcome !