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.
In your view, v6 must tunnel to v4 to exchange email. This suggests a
need for translation services to deal with those not prepared for v6. :^)
No tunels, gateway. The MTA speaks v6 to the local SUBMIT and POP
users, and v4 to its SMTP peers.
How would one vet email sources over v6 from other geographic regions?
Personally, I wouldn't even try.
R's,
John
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