Got the ISO last night, installed it over my previous, hand-built test server, and its up and running and happily relaying mail once again.
It has the same bug that server-manager had on my previous server, the one where the e-mail panel wont open and gives an 'Internal Server Error.' But since server-manager is being replaced with smanager, this is not an issue. At least I'm relieved to know that the bug wasnt caused by something I did.
I did get a warning email last night saying:
'Cannot query quota for 'compdoc' on '(XFS)/dev/mapper/kss_rocky-home': No quotas on this system.'
However as I said before, no mail is stored on this test system and no quotas were set beyond the default of zero, so this is also a non-issue.
In the meantime, I only need to add a few custom templates to complete the system. btw, I really like Roundcube even tho Im not using it yet. Great job, guys.