Which country is the smallest sovereign state to operate its own postal service?

Vatican City is the smallest sovereign state to operate its own postal service, the Poste Vaticane.

The Vatican postal system was established after the Lateran Treaty created the city-state in 1929. Vatican mail is internationally recognised, and the service issues postage stamps that are collected worldwide. The stamps commonly feature popes, religious ceremonies, artworks and major Vatican events.

Vatican City’s postal arrangements are closely connected with Italy because the state is enclosed by Rome, but the service is distinct from the Italian postal system. Its stamps and cancellations are especially popular with philatelists. The Vatican’s small size does not prevent it from maintaining separate communications institutions, just as it maintains its own postage, vehicle registration and coinage arrangements.