I use dadamail too. Have been for over 20 years. Dadamail is not to be blamed. The behaviour you describe is typical. You would see the same thing even if Dadamail was not installed on your server.
Over 100% cpu utilisation can happen even on a single core server and yours is much beefier. This percentage is not how we think of percentages intuitively.
If you are a Virtualmin newbie and wish to have a quick 10 minute paid chat about this, you could do that in addition to interacting with the very helpful community via this forum.
See