I have also used SmartOS, which imports KVM from Linux.

It is odd to boot it and see sendmail running from my native ksh93 root login.

https://www.tritondatacenter.com/smartos

https://en.wikipedia.org/wiki/SmartOS

While we do still ship KVM on SmartOS, we've moved development over to bhyve - https://docs.smartos.org/bhyve/

using our package manager pkgsrc [https://pkgsrc.smartos.org/], you can install the MTA of your choice too!