Mail boat
Mail boats or postal boats are a boat or ship used for the delivery of mail and sometimes transportation of goods, people and vehicles in communities where bodies of water commonly separate or separated settlements, towns or cities often where bridges were or are not available. They were or are also used where water transport is more efficient or cost effective or other means of transport to the destination is impractical even when roads or flights may be another option. Nearly any type or size of boat or ship may be used as a mail boat, or mail  ship, and the size of the boat may be determined by the needs of the communities it serves or by environmental factors which may influence the boats design for protection of crew, passengers, and items for transport, or requiring lesser draft for shallower waters. Sometimes a mail jumper jumps off the boat to exchange inbound and outbound mail while the mail boat continues slow movement rather than docking. Modern day use. Mail boats are still in use for some communities and may become tourist attractions, or a means of slow travel while still serving the purpose of mail transit. The  inter-island commerce of some countries depend heavily on mail boat services. In these areas the mail boat may be large enough to carry a number of vehicles including tractor-trailers.