I have been running a mailinabox email server for over a year now. You basically just run the install script, tell it your domain name and set the server as the name server for your domain name and its all done. The thing does everything for you including renewing certificates. It then sends you a monthly status email and an email whenever something needs your attention like the certbot renewal failing.

So far in the past year the only manual intervention after setting it up was updating it from ubuntu 14 to 18

There are a few tools that offer simplified mail server deployments. iRedMail, MailCow, Mail-in-a-Box, and Cloudron (does more than just mail).

If that's what you want, look at fastmail or protonmail...

This is a kind of interesting product in that arena: https://thehelm.com/

It's sort of a managed server that lives in your home. I'm not sure whether that's actually better than having your data out in the cloud or whether it's more on the security theater end of the spectrum, but it is interesting.

It’s almost trivially easy with opensmtpd IMO.

I think Debian also has a GUI for setting one up.

iRedMail rolls everything into a convenient package. The basic tier (no tech support) is free.