The SPF (Sender Policy Framework) a DNS based system that allows mail server to check that the IP address of a source of mail is authorised to send mail for a given domain. When a mail message is received, FTGate retrieves the SPF records for the senders email address and verifies that it incudes the IP address of the sending server.
SPF checking is enabled in the Security Policy of an SMTP. The result of the SPF check can also be used in the Filter Policy Rules and used to bypass Greylisting
SPF checks will not be performed for authenticated users (See Relay Control and Authentication)