i ended up doing multiple searches on different keywords and found this post:
which helped me get past the BIND DNS issue
the next issue was postfix. that led me to : A problem was found with your Postfix virtual maps : No map sources were found in the Postfix configuration
In this thread, joe states “This usually indicates your installation did not complete.”
That seems to sum up my experience. after every step, Virtualmin seemed to install a little further until, finally, everything was correct according to Virtualmin and the server is back to normal.