The FortiGate unit queries the FortiGuard Antispam Service to determine if the IP address of the client delivering the email is blacklisted. A match will cause the FortiGate unit to treat delivered messages as spam.

The default setting of the smtp-spamhdrip CLI command is disable. If enabled, the FortiGate unit will check all the IP addresses in the header of SMTP email against the FortiGuard Antispam Service. For more information, see the FortiGate CLI Reference.