upgrade mailman to mailman 3
Mailman 2 was removed from Debian bullseye, we need to either upgrade to Mailman 3 or get rid of it. This is part of the 2022-Q1/Q2 OKRs and the %Debian 11 bullseye upgrade milestone.
upgrade procedure: https://docs.mailman3.org/en/latest/migration.html
Edited by anarcat