There's also SailMail.[1] This is a minimal e-mail system for ocean sailing yachts. It uses HF radio, and there are 20 shore stations licensed in the Maritime Radio Service for connections. It's intended for boats with limited electrical power and electronics. Stan Honey, who invented ETAK, the first car navigation system, is behind it. He's into sailing, and holds the transatlantic sailing speed record.

[1] https://sailmail.com/