The Casco Bay Mailboat is a sailing vessel, run by Casco Bay Lines, which delivers mail and other items to the residents of the islands of Casco Bay in Maine, United States.

It is the longest-running mailboat service in the country, having been in existence since the 1870s.

[1] Currently undertaken by the Maquoit II, one of Casco Bay Lines' three mail boats,[1] the service runs twice daily.

[3] The route takes the boat beside landmarks such as Fort Gorges and Luckse Sound, where ships were torpedoed during World War II.

[2] The mailboat is based at the Maine State Pier and departs at 10.00 AM and 2.15 PM.