ISPConfig3 and Devuan
ISPConfig (https://www.ispconfig.org/) is an open source control panel for Linux which we use for our web hosting clients. It includes the ability to control web, mail and DNS services through a simple web interface.
ISPConfig is under active development and has a support option available for organizations who need it. The support license is very inexpensive, and I have never had a response in longer than a few hours. And, they never laughed when I did something really, really stupid.
ISPConfig has an impressive list of HowTo's, but they focus on mainstream Linux distributions, so sometimes it is more difficult to figure out what to do when you need help on something other than CentOS or Debian.
Devuan Linux is a version of Debian Linux with the systemd init system replaced with one of three more reliable inits. I have been using Devuan since Debian decided to remove support for other init systems a few years ago.
These articles are specifically for installing and using ISPConfig3 with Devuan Linux. In most cases, they are taken directly from articles at https://www.howtoforge.com/ and summarized with the changes necessary. I strongly recommend reading the https://www.howtoforge.com/ articles as they take the time to explain, whereas these are just my notes which may or may not make sense to others.