You have probably noticed that bulk mail senders often include instructions to add their message to your Safe Senders List in order to bypass future checks. Is this a good idea? Well no, unfortunately.

SPF (Sender Policy Framework) is an email validation system which uses bonded sender technology built into the Internet Domain Name System (DNS) to verify that an email has indeed come from an allowed server. It's one of the best known of the sender verification methods, which were developed in defense against the dark arts.