What is Subscription Moderation?
 

Usually, to an applicant for subscription is sent a confirmation request. To confirm it, one should just reply to the message received from the Mailing list. When it is done, recipient's address is added to the database and he becomes a subscriber. This verification mechanism tests if the person at the subscription address really wants to be a subscriber. An applicant for subscription can subscribe as well, if he send blank email to: name-subscribe@yourdomain.com, where name is Mailing List name for which that person wants to subscribe.

If Mailing list is using a subscription moderation, then the request for subscription is passed on to the list moderator(s). One becomes a subscriber only after his request has been approved by a moderator.