Tuy Hoa to Nha Trang in detail
Every city, town and village has some sort of buu dien (post office).
Vietnam has a quite reliable postal service. For anything important, express-mail service (EMS), available in the larger cities, is twice as fast as regular airmail and everything is registered.
Private couriers such as FedEx, DHL and UPS are reliable for transporting documents or small parcels.