The DKIM authentication convention could be noted at the EHLO by
having the host-name for the client utilize a "_dkim." prefix. This
prefix signals the mode of authentication made possible by the DKIM
convention claiming this prefix. This could fall into the same realm
as the key, and From policy records. There would be zero additional
transactions needed to support this form of client authentication,
assuming an A record lookup would be performed anyway. The "_dkim."
prefix can make this authentication more stringent, instead of this
being allowed to fail as currently defined in RFC2821.
I like this idea...
But not for stringency.. more for reducing the number of lookups.
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