Part of lp.registry.interfaces.mailinglistsubscription View In Hierarchy
When a person joins a team, or is joined to a team, their auto-subscribe policy describes how and whether they will be automatically subscribed to any team mailing list that the team may have.
This does not describe what happens when a team that already has members gets a new team mailing list. In that case, its members are never automatically subscribed to the mailing list.