Every other logistics network on earth gets to say no. The USPS does not. Universal service obligation means one price to move a letter, whether it crosses the street or reaches a cabin in the Brooks Range. No distance pricing, no refusing an address, no quietly dropping unprofitable routes. That single constraint removes the lever every commercial carrier pulls to keep its network tractable. The numbers set the floor: 170.4 million delivery points in FY2025, growing by roughly a million a year while volume slides from its 2006 peak of 213 billion pieces. Fewer items, more doors, rising cost per stop even when nothing else changes. Then the routing. A letter carrier is not solving the travelling salesman problem, because they are not visiting nodes, they are traversing edges. Every street segment on a route must be covered regardless of whether mail exists for it. That is the Chinese Postman Problem, formalised by Mei-Ko Kwan in 1960, and on an undirected graph it is beautifully tra...