Mail rate limiting for non-virtualmin domain

If I set the “Global message limit” to “0” mails per hour, and then set ‘Per sender domain overrides’ (with the idea that if I had neglected to set an override, a domain would be unable to send mail at)… presuming this is an email-only server, could I manually add an override for the-server-name.com (since I don’t see it as a pulldown)?

I ask because on a web-only virtualmin server when I run a scheduled backup, I am sent a report mail from root@that-server-name.com. I would still want such reports but there seems to be no way to automatically add “Per sender domain overrides” for a newly created domain (correct me if I am wrong about that, but I do not see that as an Account Plan or Server Template setting) and so I want the motivation that a new mail domain will not work till I set one (rather than using the “a spammer just hijacked an email address and sent 1,000,000 mails… oops, I forgot to set that” model), something like:

racl whitelist from /.*@the-server-name.com/

I mean.

SYSTEM INFORMATION
OS type and version Ubuntu 22.04
Virtualmin version 7.10.0