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

2008-04-17 05:24:10

--On Thursday, 17 April, 2008 13:16 +0200 Arnt Gulbrandsen
<arnt(_at_)oryx(_dot_)com> wrote:

Tony Finch writes:
On Thu, 17 Apr 2008, John C Klensin wrote:

 And, unless I misread your note, I think that puts us in
 violent agreement.

Yes :-)

(Assuming that by "lower priority MX" you mean

I agree too. IPv6 sites have to have MXes and be
IPv4-reachable somehow.

I still can't understand why so many people here think an AAAA
should suffice.

Speaking for myself and not presuming to speak for "many
people", I think the following statements are both true and that
they are perfectly consistent with each other.

(i) It would be a fairly bad idea for the protocol to require an
MX record for AAAA but not for A.  Part of my reasoning is that
some of the arguments for prohibiting implicit MX generation on
AAAA fall apart for hosts that also have IPv4 addresses, since
those addresses will cause the the MXs to be generated anyway.
And I believe that "interpret some MXs as applying only to the A
records associated with the target host while interpreting
others as applying to all address records" as leading us into a
world of confusion and harm.   I understand all of the
counterarguments and do not want to restart the debate -- no one
is likely to convince me at this point and I don't expect to
convince anyone else-- but I still, personally, reach that

(ii) It would be mildly insane operationally (or at least
stupidly careless) for someone to configure the DNS records for
an IPv6-only host without MX records that specify IPv4 access to
that host.  An exception would arise if IPv6 were being used as
a spam control technique (i.e., "if anyone can't figure out how
to send me mail over IPv6, I don't want to hear from them"), but
the benefits of such a technique would presumably be
short-lived.    As IPv6 spreads, it will become mildly insane
for the DNS records for an IPv4-only host to by configured
without similar MX records.  So I am guessing that, over the
next several years, we will see an increase in use of explicit
MX records for hosts that really want to send or receive mail,
regardless of what the standard says about implicit MXs.  And I,
again personally, consider that A Good Thing.


p.s. Thanks for the offer.  I think that would be great.