They do have a freemium mail offering https://www.startmail.com/en/ https://www.startmail.com/en/ I have no idea how much revenue this may bring in but it can

They do have a freemium mail offering https://www.startmail.com/en/ https://www.startmail.com/en/ I have no idea how much revenue this may bring in but it can't be much since I don't think I've ever seen it recommended in an Ask HN thread.