Just see it as a transaction: your email and permission to send you at least one newsletter (you can always unsubscribe) in exchange for the book. Asking for a

Just see it as a transaction: your email and permission to send you at least one newsletter (you can always unsubscribe) in exchange for the book. Asking for a download without having to give your email is a little strange, after all the book's seller is allowed to set the "price" they want.