Once you know the list name, do the following steps. In the body of the message type the single word unsubscribe. Send the message. Within 15 minutes you should get a message back saying that you are off the list. It is the subscriber's obligation to unsubscribe before you terminate your account, or change addresses.
All lists have limits.
If they did not, lists would approximate trash cans with mountains of unread messages. Our server has limits for a reason, and that is to keep things clean and readable. Here are the limits to our lists. Anything more is discarded. See note below.