Hi @mrnico,
Virtualmin is a subset of Webmin.
Webmin is a server administration system. There is no WHM equivalent of this. It allows one to control every single aspect of your server, and more. WHM is only for controlling shared hosting.
Virtualmin, the subset, allows shared hosting server and domain administration.
Usermin is just Webmail. It’s a basic interface a lot like Horde, but Virtualmin, the shared hosting administration panel, also comes with Horde and Roundcube, just like WHM does.
What you are probably trying to figure out is how a normal user would access your system, versus how an administrator would access your system.
So, a normal user, accesses their “panel” via port 10000, just like the administrator. This is different to WHM. In a WHM system the admin accesses port 2087 where the end-user accesses port 2083.
So, your normal user would log into the panel using their username and password.
Then they will have a limited view of administration capability. I guess one could say this is the same at cPanel on port 2083.
If your user like the basic interface of Usermin, which I doubt, they could log into the Webmail on port 20000, e.g.:
My personal preference is a new domain call it “webmail.ourbusiness.com” and then deploying Roundcube using the Script installer.