+++ Even a few seconds would be painfull. We process between 250K and
300K messages per day. I am hoping that number will quickly go down with
the advant of SPF but, a couple of seconds right out of the gate would be
horrible.
But what proportion of those are from a few dozen major ISP's whose
SPF records will just sit in your DNS cache?
I suspect that a large organization will build up a sufficiently rich
cache that SPF lookups will be quick.
However, that is an argument against looking up in _spf.domain, since
this domain will generally not exist, and lookups will generally be
negatively cached for much shorter periods of time than successful
lookups.
-roy
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