I've been running MiaB for about 6-7 months now. It's one of those things that 'just works', and with 'just works' I mean:

* Well configured, secure email server * Ease of adding/removing domains, aliases, catch-alls and user accounts * Ease of using email, either with the ready-to-go Roundcube webmail or any IMAP/POP client * Batteries included: DNS is included, DKIM, SPF, you name it. DNSSec * Want to host a static HTML site? MiaB's got you covered. * Yes, that included Let's Encrypt SSL certs * Awesome status page to check: version updates, misconfiguration, system health, and for each domain: DNSSEC, nameservers, DNS, TLS/SSL, blacklisting, etc. * Open source! Huzzah!

If you're serious about moving away from Google or any other corporate mailprovider is feasible, take a look at Mail in a Box.