The mailman 3 suite is a re-write of mailman 2. It now has LDAP / OpenID support!
Migration is possible, but not trivial (archives may break, but our mailman 2 archives are broken anyway): http://docs.mailman3.org/en/latest/pre-installation-guide.html#how-can-i-upgrade-from-mailman-2-1-x
Installation via Docker or from Debian repo.
We should investigate when/if/how we should do the migration.