You can enable SPF checking in SpamTitan via System Setup -> Mail Relay -> Sender Controls.

SPF allows the owner of a domain to use DNS records to specify which ip addresses are authorized to transmit e-mail for that domain. When receiving a message from a domain, SpamTitan can check the DNS records to make sure that the mail comes from an IP addresses that the domain authorizes.

Enabling SPF will only affect mail from domains with an SPF DNS record. Mail from domains with no SPF record will be unaffected.

More information on SPF can be found at