Chapter 15 Unified Threat Management for FortiOS 5.0 : Email filter : Email filter concepts
  
Email filter concepts
You can configure the FortiGate unit to manage unsolicited commercial email by detecting and identifying spam messages from known or suspected spam servers.
The FortiGuard Antispam Service uses both a sender IP reputation database and a spam signature database, along with sophisticated spam filtering tools, to detect and block a wide range of spam messages. Using FortiGuard Antispam email filter profile settings, you can enable IP address checking, URL checking, email checksum checking, and spam submission. Updates to the IP reputation and spam signature databases are provided continuously via the global FortiGuard Distribution Network.
From the FortiGuard Antispam Service page in the FortiGuard Center, you can find out whether an IP address is blacklisted in the FortiGuard antispam IP reputation database, or whether a URL or email address is in the signature database.