Virtualmin to Virtualmin PRO Upgrade?

This is actually one of the issues that I'm working to resolve before the release. We do want to provide a clean upgrade path, but because Virtualmin is so flexible. i.e. it can use Sendmail, Postfix, QMail, as well as allowing a very wide range of options that aren't necessarily changeable without causing some conflicts. When changes are made, it's usually easy to manually correct any issues that pop up, but for a server with many domains it could be a painful process--and we're going to be supporting folks in the migration process as part of the cost of purchase, so we want to make sure that support doesn't suck up all of our resources.

It is likely we will offer a "minimal" Virtualmin Professional installer that does not change any existing configuration--it just adds the new features and plugins. This would mean that some aspects of the system would be unavailable until manually enabled (like anti-spam and anti-virus, which requires some tricky Procmail rules). It just isn't safe to go around altering peoples production systems in that kind of way...but we've tried to provide automated mechanisms to add these things in after the installation without any hassle--thus, if you know you don't have anything out of the ordinary in your Postfix configuration and you don't already have anti-spam and anti-virus products installed, it will be easy to set it up after the install.

In short, our position is that upgrades are definitely supported--even if it means one of us has to hold your hand through the process of making it work--but there might be some effort required from both you and us. Hopefully, we can minimize the need for that by adding migration tools that are automatic and fool-proof as we become aware of issues that are not currently handled.

Hope this answers your question (a very good one, too...I've heard it privately a few times, so it's good to get it out here...I'll add it to the FAQ as well so it's easy to find).