the thing can run on your premises completely

lighthouses that do the initial intros

Sounds like these lighthouses must be provided by somebody else which makes it not entirely on my premises anymore.

The cheapest Infomaniak tier is about 25€ per year. The sign up process is a bit confusing because by the end you have like 3 passwords or something but once you get it going it’s a decent service. I don’t use it myself but I set it up for my parents and after initial setup it has been working without issues.

https://www.infomaniak.com/en/ksuite/service-mail

Wait I don’t understand how changing your CNAME to A records resolved your problem. Did your wife’s computer simply not resolve the CNAME records?

Ubuntu Pro gives you 5 more years of security updates for versions that are EoL. You can see it here if you scroll down to the maintenance schedule https://ubuntu.com/security/esm