I think this new...
If there is a reasonable way to do it, it might be useful for receivers to
be able to get a hint before going to DATA if the message is going to be
DKIM signed. I can envision looking for such a hint when evaluating a
message from an IP address listed in an RBL and perhaps going to DATA to
look for the promised signature.
Such a hint would, I imagine, only be useful when From = Mail From. IIRC,
that accounts for about 80% of mail.
If the information (such as the policy record perhaps) contained a list of
authorized signing domains then a receiver could go to DATA and find out if
it was worth expending the CPU cycles to verify.
I can see some potential for this to make signing more attractive to small
senders who are more likely to be blocked due to RBLs. It may be
attractive to receivers as a way to reduce false positives from spam
filtering techniques used on the envelope.
Scott K
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