Which of the following email spam filtering features is NOT supported on a FortiGate unit?

FortiGate supports MIME Header Check to inspect the headers of email messages for suspicious or malformed content as part of its anti-spam and content filtering capabilities.

HELO DNS Lookup is a supported FortiGate anti-spam feature that verifies the hostname provided in the HELO/EHLO command against DNS records, helping to identify spoofed or invalid senders.

Greylisting, which temporarily rejects emails from unknown senders forcing legitimate servers to retry, is not a native anti-spam feature directly implemented on FortiGate units for SMTP traffic; it is typically found in dedicated anti-spam appliances or services.

FortiGate units can perform Banned Word filtering, allowing administrators to configure custom lists of words or phrases that, if found in email content, will trigger a spam action.