No unsubscribe options as of now. For now, its left to the dev's discretion to not send annoying emails.
Though this sounds like a feature of a more managed solution. I know MailChimp has this out of the box (and possibly other providers).
Since this library is supposed to provide email automation capability, I'm not sure options like Unsubscribe should be part of the library.
What do you think? Definitely open to ideas.