On Sat, Dec 4, 2021 at 2:35 PM Douglas Foster < dougfoster.emailstanda...@gmail.com> wrote:
> I think this text was inserted because of an open ticket when discussion > was going nowhere and a new draft was created. Perhaps the originator of > that ticket can elaborate on his thinking. > I believe the admonishment against best-guess SPF was based at least in part on the sentiments found here: http://www.open-spf.org/FAQ/Best_guess_record/ ...which is to say it's apparently a discouraged practice. It makes it difficult for DMARC to be deterministic when the things upon which it's built behave in unpredictable ways. That's not to say this is unique though; DKIM, for example, allows verifiers to decide what an acceptable signature is (a favorite I remember from the early days was "I don't want to accept a DKIM signature that didn't cover the Subject field"), which again means one site's "pass" is another site's "fail". -MSK
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