Something is weird about email: Everyone can pretend to be someone else. It would be sane to reject all emails from a domain, that has no SPF record. I was asthonished when i realized that this is not already happening. Designing a large communication system it is just pure insanity to not include a sentence like this in the spec: "One can only send messages as one of the names he has power over." This could be ensured simply by SPF. It should be safe to assume, that a domain that has no SPF-record is not used for sending emails. I know that this is not the case right now, but it would change really fast, if you would push an update to the SPF-checkers, to enforce that rule. SPAM would be much less of problem than it is right now. Today you have to block ip-addresses, which is a large mess. With this rule enforced, you could block domains. Which are much harder to obtain and have a way smaller quantity.