--On Thursday, 17 April, 2008 11:25 +0100 Tony Finch
<[EMAIL PROTECTED]> wrote:
> On Wed, 16 Apr 2008, Willie Gillespie wrote:
>> Tony Finch wrote:
>> > On Wed, 16 Apr 2008, Ned Freed wrote:
>> >>> I doubt that it makes sense to accept email from
>> >>> [EMAIL PROTECTED] on a system that can only
>> >>> communicate with IPv4 addresses.
>>
>> I foresee some company setting up an IPv6 to IPv4 e-mail
>> relay for individuals or other companies that only have IPv6
>> addresses.
>
> I agree with John that this is likely to happen.
>
>> For an IPv4-only receiving system, would this appear as an
>> e-mail from [EMAIL PROTECTED] (even though it comes over
>> the IPv4 link)? At that point, would it make sense to accept
>> the message?
>
> The sender's relay has to be two-way, so the IPv6-only site's
> MXs would have to refer to the relay's IPv4 address as well as
> the site's own IPv6 address. Then the sender's email addresses
> can be verified successfully by IPv4-only sites.
>
> I don't think John is right to expect IPv4-only recipient
> sites to obtain a 4-to-6 SMTP relay service any time soon.
> IPv6 sites will have to deal with the interop burden until v4
> is the minority.
>
> For example, there are likely to be problems if
> [EMAIL PROTECTED] AAAA-only addresses leak out, and these
> are likely to be worse than the problems that A-only addresses
> like [EMAIL PROTECTED] have.
Whatever I said, I didn't intend it to convey the expectation
that the responsibility would need to lie with the IPv4-only
recipient site. I have come to believe that it is appropriate
for a receiving site to do at least superficial verification of
the possibility of delivering an NDN before accepting a message
for delivery for which an NDN might be necessary (i.e., for
which delivery cannot be assured while the SMTP connection is
still open). I think that testing the reverse path and making a
decision to not accept the message if the test fails is entirely
consistent with the "take responsibility" language of 2821 (and
1123).
I think that implies that, for the near future at least, if
[EMAIL PROTECTED] wants to have a reasonable expectation
that mail it sends will be accepted by mail servers running in
IPv4-only environments, then it (the sender) must expect to
either be dual-stack (and advertise the IPv4 address too) or to
have a lower-priority MX advertised that will accept IPv4
traffic.
And, unless I misread your note, I think that puts us in violent
agreement.
john
