Honestly the wiki is excellent, I do recommend to dive in head first with the install guide

Thunderbird

It is bot the most feature rich and the most annoying thing, but it works

The issue is that it is simply not built with reliability as a high priority so probably some hardware component shits itself too much after a while.There is a reason every reasonable company that needs a server to run reliably in production uses something orders of magnitude more expensive than a rpi.

You lucked out with your previous experiences, but many others did not, or the industry would not pay the price of a rpi a month to run a machine with the specs of a rpi.

That said, if you don’t need the reliability some easy hacks like a reboot cronjob or systemd timer, or trying to turn off unneeded services or peripherals could give you 90% of an industrial server’s reliability