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.
Q35872
boat
Concept
Q11446
ship
Concept
Q49845
mail
Concept
Q155930
water transport
Concept
Q6735720
mail jumper
Concept
Q96391554
Mail boat
UNK
different from