Chapter 15 Unified Threat Management for FortiOS 5.0 : Email filter : Email filter concepts : Order of spam filtering : Order of IMAP, POP3, IMAPS and POP3S spam filtering
  
Order of IMAP, POP3, IMAPS and POP3S spam filtering
The FortiGate unit scans IMAP, POP3, IMAPS and POP3S email for spam in the order given below. IMAPS and POP3S spam filtering is available on FortiGate units that support SSL content scanning and inspection.
1. MIME headers check, E-mail address BWL check
2. Banned word check on email subject
3. IP BWL check
4. Banned word check on email body
5. Return email DNS check, FortiGuard Antispam email checksum check, FortiGuard Antispam URL check, DNSBL & ORDBL check.