This is not an official python ProtonMail API client. it allows you to read, send and delete messages in protonmail, as well as render a ready-made template with embedded images.
new_message = proton.create_message(
recipients=["to1@proton.me", "to2@protonmail.com," "to3@gmail.com"] ,
subject="My first message",
body="<html><body>hello, i sent my first mail!</body></html>"
)
sent_message = proton.send_message(new_message)
now you can send messages to proton addresses: