It’s time to pay off some technical debt!
I have been running an email server since forever. Way back in 2004 I switched Linux distros to the newly-hatched Ubuntu. There were things I liked about it, particularly when they started offering long-term support (LTS) versions that would receive updates for years. I was running Postfix for the MTA and Dovecot for the user-facing side, and everything went really well. Every two years, a new LTS release of Ubuntu would come out, I would upgrade and spend most of a day cleaning up the inevitable rough edges, and Life Was Good™.