This runs from a small box with everything included. It gives you all the tools and config needed for running a secure and feature rich email service. Webmail, some sort of exchange emulation, webcalender on top of a solid postfix/dovecot install with rspamd as spam filter. Everything is configurable via a nice web UI.
After 15y running my own mail service and editing a lot of config files, I use this piece of free and open software and find it very good. All you need is a box somewhere in the internet. Running from a homelab will instantly fail, expect you have a static ip.