That's a good start. Now we need to figure out some way to find out
who's doing those lookups, and what they're doing with them.
It should be fairly easy to figure out how many unique IP addresses are doing
the lookups, and give some view of the distribution. And then not too hard to
figure out how many of those IP addresses don't belong to the top 5 or so
mailbox providers.
That would be of some help, but the real question is what they're doing
with it after they get it. The top mailbox providers presumably have
reasonable DNS caches, so their lookups will be imperceptible anyway.
Since few people in the world at large understand DKIM, much less ADSP,
the large numbers of lookups that Brett reports must be coming from
software packages that have a configuration that looks them up. It might
be possible to intuit from the details of the lookups, e.g., the sequence
of queries, what packages they are, at which point we could probably look
and see what they're doing with them.
If paypal want to broaden the uptake of ADSP, then contributing DKIM/ADSP
code or config recipes to open source MTA projects would be useful!
There's ADSP code in Spamassassin for anyone who wants it. They suggest
that you configure it to ignore actual ADSP and hard code a handful of
domains such as paypal.com and ebay.com.
R's,
John
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