why do some mailing lists have two or more addresses associated with them, and what are they used for?

Answer 1

Most mailing lists have at least two addresses: one for sending messages to the list and one for administrative requests. You send email to the admin address to subscribe, unsubscribe, change to or from digest mode, etc. Sending these requests to the message address for everyone to see will get you flamed, or at least laughed at.