Dear Jonathan Mitchell,
@ is the special syntax to recognize an email. This is the reason we could not filter a sub-domain like your suggestion *@*.domain.com.
So we need to add a new [Email Domain Ban Filters] feature in our future release (where admin can filter by sub-domain).
If you want to track the status of your suggestion, please submit your suggestion to GIThub https://github.com/PHPfox-Official/phpfox-v4-feature-requests.
Regards,
Hannah
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