SMTP SPF: What SPF Is And Is Not: "Standard SMTP email is anonymous and forgeable. SPF closes this loophole. SFP is primarily an anti-forgery effort. Any benefits in the area of reduced spam, worms, viruses, etc are pleasant side-effects. That said, if SPF causes spammers to send mail from their own domains, we'll be better able to identify and block those domains."  10:03:30 PM