2 questions

Hi! I've got 2 basic questions I'd really like an answer to. I'm new at this, so please forgive my ignorance: 1. How can I prevent non-subscribers from posting to a list? 2. Every time a subscriber sends an unsubscribe request, the answer is: "You have not been removed, I couldn't find your name on the list." In every case, the name IS on the list. I'd really appreciate any help I can get. Thank you in advance :-) Kind regards, Anne-Marie Oualit