That’s one of the places your configuration could be different from what Virtualmin sets up, and an area where you may be missing a bunch of Virtualmin features after importing them into Virtualmin on an existing system.
But, also email is a big area with possibility of wild divergence and where Virtualmin installation could either break your existing configuration or simply not work or both. (And, now that I’m thinking about how different your mail configuration might be, I am inclined to discourage you from trying to install on a production system with even more gusto. At least installing with the install script, since it pulls in a bunch of dependencies that might conflict with the software you’re actually using and thus force the software you’re actually using to be removed.
The way Virtualmin does things may be completely foreign to your system, or look very similar. I can’t guess how you think about problems like virtual hosting. Did you put each site in its own home dir and give it its own user for security? Virtualmin does. Did you pick Postfix and Dovecot for your mail stack? Procmail for delivery agent, or something else? All of these differences can be worked out (and Virtualmin supports a bunch of other configurations and services…this is just the default stack we install).
I’ve made my recommendation: Install Virtualmin on a fresh system and migrate your sites at your leisure and with zero risk.
I can’t imagine managing a full-featured web hosting system, with mail, databases, apps, etc. without Virtualmin. I mean, I can do it, of course, and I have done it, it’s just a lot of wasted hours that could be automated away.
But, if the choice is between “keep doing what you’re doing” and “possibly do a bunch of destructive actions to your existing system”, then just keep on keeping on.
You can see what the Virtualmin install script does, if you want to run through a checklist of what software will be installed (and what that means for what you already have installed and depend on). Check the deps in GitHub - virtualmin/virtualmin-yum-groups: Group definition files for yum/dnf used by virtualmin-install on CentOS/RHEL/Fedora or GitHub - virtualmin/virtualmin-lamp-stack-ubu: Ubuntu metapackage that depends on the LAMP stack for Virtualmin
The middle ground would be just to install the
webmin-virtual-server module, just so you get the core Virtualmin functionality in Webmin without installing any of our dependencies or any of our post-install configuration. That’s entirely safe, but only gets you a small portion of the Virtualmin experience (but the most important part of it for a lot of users…the virtual host and user and database management, though you probably have to do some configuring to make it all actually work).
Honestly, I think you’re trying really hard to make a lot of extra work for yourself, and I can’t condone that sort of thing. I think you’d save time and heartache by starting with a fresh OS, and importing your websites at your leisure.
I suspect a lot of the stuff you found difficult or fiddly to get working probably won’t be with Virtualmin, assuming it’s a full Virtualmin system installed on a fresh supported OS.architecture.