SPF/DKIM is really about mail server reputation. So it mostly benefits larger servers like the ones run by Google, Microsoft and Yahoo. Unfortunately, that means that attempts by those larger providers to combat spam using such reputation will naturally hurt smaller providers. So the actual effects of SPF/DKIM are on the whole negative.
The root problem is that we don't actually need to keep track of email server reputation. No one says to themselves "Huh, this is from a Gmail address, it must be legit". We really want to keep track of sender reputation. We need to be able to treat anonymous email differently than email from people we actually know. That implies that we have some work to do on the problem of identity. As it is, there is not even a way for a known email sender to securely introduce an unknown email sender. You know, the way that regular human people normally are able to transfer identities from one to the other.
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