While I'm just catching up on this thread, I can also chime in that --
as far as I can tell, neither spf or dkim has had any impact on spam,
at least from what I can determine.
If that was the original intent of spf and/or dkim, then I would be
inclined to say that neither have properly addressed the spam problem.
I can't speak for the SPF crowd, but the goal of DKIM is to make it
easier to recognize mail from people you know, for some definition
of "people" and "know" which should make filtering more accurate.
It's also alleged to be useful to deter forgery, although I happen
to think that any forgery it deters is already covered under the
category of mail from people you don't know.
The only thing that's going to make the amount of spam drop is major
legal and technical advances that get rid of botnets. Don't hold your
breath.
R's,
John
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