v6 white-listing takes renumbering to a horrific place and might work
only during an initial transition where the number of v6 only sources
are few. Over a period of a few years, these numbers are likely to
explode into millions.
Why? The estimates I seen say that there are about 100,000 legitimate
mail emitters. I do agree that there is not an obvious way to use the
DNS to find 100,000 addresses within the v6 address space without
blowing away DNS caches.
Why not offer v6 to v4 tunneling where there is truly zero tolerance for
unsolicited commercial email?
I still don't see any practical reason to exchange mail over v6. Even
assuming all the consumer ISPs move their customers to v6, those
customers will be talking to MTAs or web mail over v6, which can then
use v4 to talk to other MTAs. Given the small number of legit mail
sources, I find it hard to believe that the cost of finding some v4
address space would be an insurmountable problem for anyone whose mail
I wanted to receive.
R's,
John
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