A couple of other things I tried:
- rebooting server (made no difference)
- created a new dummy virtualmin server (domain account) (worked!)
Creating a new dummy server/domain via Virtualmin > Create Virtual Server seems to have fixed the issue. So my guess is something else needs to happen to complete the process we put together in this thread: How to configure SSL for Dovecot/Postfix manually? - #18 by Brook
I would guess that something needs to be copied to the Postfix config to make it aware a new cert has been created - any ideas if that’s the case? If so what are those steps?