Hardening unused (sub)domains - Mailhardener knowledge baseHardening unused (sub)domains Even if a domain is not intended to be used for email, whether it being inbound (receiving) or outbound (sending) email, it is still recommended to apply proper email hardening techniques to prevent the domain from being abused for fraudulent activities. Domains that are not used for email may be parked domains, legacy domains, testing domains, black-hole domains, or
