[ietf-dkim] Are lookalike domains like parent domains?

[Tony Finch]

On Wed, 30 Apr 2008, Arvel Hathcock wrote:
>
> Enter the NXDOMAIN check.  If, as part of the ADSP algorithm, an
> NXDOMAIN check is performed, the algorithm can quickly detect that the
> domain doesn't exist and that _this_ might be the reason there is no
> ADSP record.  This added insight closes the hole and can be used by
> filtering agents.

NXDOMAIN is the wrong check. A domain is not a valid mail domain if it has
neither MX nor A nor AAAA records. If it has a TXT record then a lookup
will not return NXDOMAIN even though it is not a valid mail domain.

Tony.
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