With mailcow [0] it's pretty simple to setup your own email server in about half an hour with all the security included and having your email not being treated on reception as spam. It also ships with a webmail interface (SOGo [1]), rspamd UI and an admin interface for your server.

I used to be a Kolab [2] user and "promoter" for many years but the project seems stalled a bit recently and although it is still being worked on and developed, it is lacking documentation for the latest releases.

I have moved to mailcow recently and am amazed at how easy it is to setup and maintain as opposed to Kolab.

The thing I miss from Kolab in mailcow is the integrated LDAP storage and custom built UI (if anyone knows a good and reliable LDAP administration UI as a web app, please let me know!), which I got used to using for user authentication in other services. Luckily, there are some efforts in LDAP integration into mailcow [3], although, still not mature yet and not that tightly integrated.

[0] https://mailcow.email/ [1] https://sogo.nu/ [2] https://kolab.org/ [3] https://github.com/Programmierus/ldap-mailcow