I'm using the Perl reference implementation of SPF.
My understanding of "best guess" was that it would pretty much convert "none"
responses into either "pass" or "neutral" depending on the MX/A record checks
it performs. Following are my test results:
Without Best-Guess
fail 1.37%
softfail 0.54%
neutral 1.48%
unknown 3.57%
error 0.07%
none 89.19%
pass 3.79%
With Best-Guess
fail 1.30%
softfail 0.52%
neutral 46.51%
unknown 0.13%
error 6.19%
none 0.00%
pass 45.35%
As expected "none" went to 0%. Most of the messages that had been "none"
appear to have would up in "pass" and "neutral". "error" also increased - I
presume this is because additional errors were generated resolving the MX/A
records. What I don't understand is why "unknown" decreased. Does "best
guess" apply to domains for which there was an error retrieving their SPF
records in addition to the ones who do not have SPF records?
Thanks,
Philip