Chapter 15 Unified Threat Management for FortiOS 5.0 : Email filter : Email filter concepts : Email filter techniques : FortiGuard email checksum check
  
FortiGuard email checksum check
The FortiGate unit sends a hash of an email to the FortiGuard Antispam server, which compares the hash to hashes of known spam messages stored in the FortiGuard Antispam database. If the hash results match, the email is flagged as spam.