Appendix A. Sender Policy Framework

Sender Policy Framework (SPF, formerly known as Sender Permitted From) is a method where domains list what IP addresses will originate email messages for the users in their domain. In this way, spammers won’t be able to use a MAIL FROM address of any domain that uses SPF and any potential recipient who is enforcing SPF checks.

SPF can be very effective at reducing spam, although it is a relatively new concept and has not been widely adopted. At the very least, a domain can use SPF to run content filtering checks (such as Bayesian analysis) on email messages that weren’t sent from SPF-verified domains. In this way, the expensive Bayesian and other such content checks can be run on messages that originate from ...

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