It's in RFC 6686, in the unlikely event that someone who cares
didn't already know the answer.
Yeah, but, knowing that, my version of Scott's comment would
have been only slightly different. (Almost) too late now, but
why wasn't this action taken as part of adopting 6686 and
documented there? If that was an inadvertent omission, ...
My recollection is that our focus was on getting SPF but not Sender-ID
from experimental to standards track. At the time I think there was still
some grousing that sender-ID wasn't entirely dead, and I don't think
anyone was willing to engage in another fight to move it to historic.
It does seem wrong that 6686 doesn't say that it obsoletes 4405-4407.
Perhaps that's the erratum. The experient is over, so there's nothing to
move to historic.
R's,
Johj