Sender Policy Framework

"Best Guess" SPF Record Check Should Be Avoided

Early in the SPF project, the idea of guessing what a sender's SPF record might be was suggested as a workaround to lack of early deployment of SPF records. This is still described in the old (circa 2005) SPF developer recommendations. Whatever value this test might have had early in the project, it has long since passed and should be avoided.

Even early in the project, this was recognized as a hack and was never standardized.

An SPF record is a statement of policy by a domain owner. Guessing in the absence of such a record reduces the reliability of SPF results. Don't do it.