When a German art dealer living in the US returns to his native country he finds himself attracted to Nazi propaganda.
A good example of a 'B noir' movie which, according to Derek Smith on Slant:
… invited on-the-fly creativity from their makers, and their oft-gritty sense of urgency allowed them to stand apart from their slicker, more star-driven “A” counterparts. The feverish intensity of many B noirs is also typically matched with a briskness and efficiency bred from the pragmatic necessity of having to clock in under 90 minutes in order to fit into the second half of a double bill. And in no small part because the studios behind these films were mostly concerned with filmmakers coming under budget and producing work as quickly as possible, the men and women behind the camera were often freer to address a more diverse array of subjects that the more prestigious studio noirs typically weren’t able to touch.
Outside of its noir-specific sensibilities, Address Unknown is very much a 'B'-budget movie: just look at the overuse of letters to convey both outward exposition and internal thoughts as well as the near-identical scenes of someone going to pick up said mail to pad the running time. Thematically, then, it's both remarkable (see below) and unsubtle at the same time, especially in its use of stigmata and other Christian imagery in order to convey the persecution of Elsa Schutz. Also of note is the chalked 'J' on the wall: this is surely a reference to Fritz Lang's M (1931), another film that is, I might add, about the rise of Nazism. Still, much to admire in Address Unknown, and I can't really put it better than Derek by quoting that the film:
… is particularly fascinating for its candid depiction of the lure of propaganda. The film resists the temptation to lean into the cheap nationalistic pride that defined so many other wartime pictures. In fact, the main character’s transformation specifically addresses the dangers of blind nationalism […]. Address Unknown is also the very rare film that delves into the humiliation faced by the German people in between the two World Wars and how it paved the way for Hitler’s rise to power.