Many other guides dive deep into 10 plus pages of how to set up such a service with Dovecot, Postfix and a web server all from the command line, but this one is a lot simpler because most of what you need is inside Citadel. Citadel also has calendar, Contacts, Notes, Tasks and chat rooms so can be a good alternative to Google or other providers. Your only cost really is the Raspberry Pi and a domain name if you don't already have one.
You could tweak this a bit further by using your own DNS provider (or alternative to Cloudflare) and considering an external hard drive connected to the Pi for reliability.
See
Raspberry Pi Email Server using Citadel#
technology #
email #
privacy #
raspberrypi #
alternativeto #
opensourceBuild your own email server on the Pi.