Knowledgebase

SPF, or Sender Policy Framework, is an anti-spam technique that takes advantage of the fact that nearly all abusive e-mail messages use fake sender addresses. The technology helps mitigate spam by providing the world with a record of who is allowed to send mail from a given domain name. Mail servers that implement the Sender Policy Framework check the source of each incoming message against the authoritative SPF record published by the sender's domain. If the source of the message is not listed in the SPF record, the message is treated as spam (generally, this means it will be directed to the recipient's Junk Mail folder).

For more information on SPF and how it works, see http://www.openspf.org/Introduction

SPF allows servers to discard messages that fail SPF checks (SoftFail or Fail) as these are probable or definite forgeries, making them spam by definition.

A Neutral or Pass result, however, says nothing about whether the message is unwanted, so no decision can be made about the spam status of the message. In other words, the "correct" server for a domain name can still send junk mail.