A vintage 1970s technical illustration showing an intricate network of pneumatic tubes and brass pipes connecting ornate Victorian-era mailboxes, with some tubes flowing smoothly while others are kinked and tangled, colorful envelopes and parcels visible through transparent glass sections of the tubes, warm sepia and copper tones, crosshatch shading technique, aged paper texture with slightly yellowed edges, mechanical gears and dials visible on junction boxes where pipes meet, steam wisps escaping from connection points, birds-eye perspective showing the complex routing system sprawling across the frame.