The system used on teams.debian.net is different to the one currently used on lists.debian.org. In fact, part of the aim of the teams.debian.net project was to 'test-drive' a new setup which could then also be used on lists.debian.org.
The mailing list manage in use on teams.debian.net is Enemies of Carlotta or EoC for short, with a few patches to change some of its behaviour, namely dealing with spliting up the different role accounts associated with a list.