I see. I suppose then I might be wrong. I myself have tried subscribing to some authors but do not recall having been asked if I want to share my email. Though perhaps it's in the settings still - will need to look into this. In any case, it's very confusing as a whole.

EDIT: having looked at the settings, I've found that there is an option to "Receive Emails from Writers" you've subscribed to. Perhaps this is what it means to "opt in" ? It's unclear if turning this off means your email can't be exported by the writers you've subscribed to.