A closed
list is one in which membership is not
automatic.
In a closed list, the list administrator, a person assigned to oversee one or more mailing lists, can either reject or
accept your request to become a
member.
The list administrator might reject your membership request if the list has too many members or if you are not part of
the groups specified
community.
Most lists are open lists that automatically accept all members, in which case the list has no administrator.