Is it permissible for an "Email to a Friend" service to simultaneously send the recipient the sender's name, email, and the friend's email, without the message text itself, and is this considered espionage?

What you want to know from the sender's email and his friends, in terms of private information, you are not permitted to obtain without the owner's permission. Otherwise, obtaining it would be considered espionage. Furthermore, there is no necessity for you to access it in the aforementioned service.