Hi Hayden,
Unfortunately, we don’t have an option that restricts emails/domains like Google, Yahoo, etc in macOS. However, we do have a restriction that disables iCloud Mail from syncing with iCloud. If you navigate to Policies > macOS > Restrictions > Allow iCloud Options and uncheck the option iCloud Mail, the Mail App will not sync with iCloud on associated devices. I’ve attached a link for the corresponding help document on macOS Restrictions for more clarity.
To add on to @paxton___’s suggestion about iOS, there is also an option to configure unmarked email domains. However, managed domain is supported only on iOS and not Mac.
We hope this answered your query. Please get back to us if you have any further questions.
Regards,
Patrick Zimmerman
Hexnode UEM