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Re: I-D Action:draft-klensin-rfc2821bis-10.txt

2008-04-21 01:59:01

On Wed, Apr 16, 2008 at 04:45:07PM -0400, John C Klensin wrote:

--On Wednesday, 16 April, 2008 14:31 -0600 Willie Gillespie
<wgillespie+ietf(_at_)es2eng(_dot_)com> wrote:

Tony Finch wrote:
On Wed, 16 Apr 2008, Ned Freed wrote:
I doubt that it makes sense to accept email from
test(_at_)ipv6(_dot_)l(_dot_)google(_dot_)com 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

Very likely, IMO

For an IPv4-only receiving system, would this appear as an
e-mail from test(_at_)ipv6(_dot_)l(_dot_)google(_dot_)com (even though it 
comes over
the IPv4 link)?  At that point, would it make sense to accept
the message?

Sure.  The problem arises if the receiving IPv4 host tries to do
some sort of sender-accessibility or callback verification.  It
won't be able to reach the IPv6 host (or send NDNs to it) unless
it either it is configured to submit those messages via an
IPv6-capable gateway or the IPv6 host advertises IPv4 addresses
(perhaps via a conversion relay in a low-preference MX record).


The host needs an A record, or an MX record which points to at
least one A record. There's no point in relying its AAAA record
to act as an implicit MX record, not as long as there are hosts
out there which have no clue about IPv6.

From my perspective, you agree with:
Date: Sat, 5 Apr 2008 14:26:50 +0200
From: Alex van den Bogaerdt <alex(_at_)ergens(_dot_)op(_dot_)het(_dot_)net>
To: ietf-smtp(_at_)imc(_dot_)org
Subject: Why implicit MX is a bad idea for IPv6