Mailing list members are people that have registered for a given mailing list to get regular email messages, including weekly newsletters. If the app that is used to manage the list permits it, you can also include mailing list members manually, but in this case such emails may be regarded as unsolicited and reported as spam by the users. Usually, these members can unsubscribe from a mailing list by clicking on a link in the messages they receive, or you, as the mailing list moderator, can manually remove them if they make such a request or in case you decide that some of the members should not be part of the mailing list any longer. Each member will be able to view only their own address in the "To" field of the messages they receive, but not the addresses of the other mailing list members.