- iredmail – seems good
https://docs.iredmail.org/install.iredmail.on.debian.ubuntu.html
- Integrate email server with next cloud tutorialhttps://123qwe.com/tutorial-debian-10/
- https://modoboa.org/en/ seem simple
- Mail-in-a-Box Setup Guide (mailinabox.email)
- Download Zimbra Collaboration Open Source Edition
