VM/CMS is very much alive and well, thank you. It is now known as z/VM and runs on the IBM z series mainframes
You can even run Linux in z/VM virtual machines now as well as CMS.
There is an emulator available, called Hercules
And an old VM/CMS is available for free, with source
Sendmail may be safely run set-user-id to root. -- Eric Allman, "Sendmail Installation Guide"