Really depends on what you want to get out of your server. Most easy to use server software I know seems to be geared towards personal use and small organisatio

Really depends on what you want to get out of your server. Most easy to use server software I know seems to be geared towards personal use and small organisations. Mail-in-a-box still works, though last time I checked they were on quite an old Ubuntu LTS release. There are a few pre-packaged docker containers too (i.e. docker-mailserver) which seem to be popular. I myself use Mailcow, but that's pretty heavy for "just" a mail server. There's also a mail server that I can't for the life of me remember the name of, which packaged a whole bunch of stuff into one single binary you can run rather than use the classic "every part of the email delivery chain is a separate process" approach. I think it was written in Go?