Space Postal Service

The distances between stars are too vast for direct radio and digital communication. Instead, spacecraft must actively courier data between worlds. This means that on frontier worlds, any visitor bringing news, stock prices and currency rates is very welcome and their data is in high demand. Each major world maintains its own decentralized digital currency because ledgers can't propagate fast enough at even interplanetary distances. This means that digital currency exchange is a huge industry, and arbitrage opportunities can be enormous. In addition, communications can't be shielded or protected except via encryption, which requires either key-exchange or delivery of one-time-pads. The space postal service provides fast, regular, trusted delivery of purely digital information to most major settlements.