I just picked this thread up as others did when searching to find out if this feature already exists. However, I don't just see this as a "nice to have" - this would be a "deal winner" for me to move to Premium. With just a single email address, I can't effectively use this across both personal and work. Toggling between email addresses just isn't practical so I'm stuck with copying and pasting. Ideally, I agree that assigning a default email address to a notebook would be great. Alternatively the ability to choose your email address when you share the note.