Consider asymmetric case of member list (list of persons who can post) and recipient list. Firstly, remove primary_member_maps from $member_maps. Instead, add $ml_home_dir/members-mailmag who can post to $member_maps. member_maps = $ml_home_dir/members-mailmag In this case, when a new user is subscribed, the user address is added to both $ml_home_dir/members and $ml_home_dir/recipinets. But $member_maps is defined as $ml_home_dir/members-mailmag. $ml_home_dir/members is not used. Hence, recipients is updated but the list of posters is unchanged. Strictly speaking, this configuration is not enough safe. If somebody fakes From: address, he/she can post since fml checks only From: address.