This tutorial will go through mailman3 installation with postfix in a Debian OS. It assumes that postfix (a Mail Transport Agent, aka MTP) and mailutils are already installed in the system and configured, and the system can send emails, e.x root user is sending admin related emails. It also assumes that python3, postgresql and apache2 are installed in the system too.
**A. SSH to the remote server**
enter root user and do a system update with apt update && apt upgrade. Install dependencies: