current usage of AAAA implicit MX?

Michael Taht m at
Tue Apr 15 04:42:06 CEST 2008

SM wrote:
> I'm assuming that a number of email sites over in Asia are already
> IPv6-enabled, and there are probably other enclaves as well. So I'm
> looking for information on actual email deployment and sites.
I implemented three ipv6/ipv4 dual stack email servers a while back. The
ONLY connections I've ever seen on it from the public internet have been
IPv4, except from my own machines.

My principal problem with implementing dual stack email has been with
STARTTLS certificate support. At the time I hadn't (still haven't)
figured out how to create a postfix cert that was correct for both


Originally I went with mx records specific to the ipv6 and ipv4, ie:

MX 10
MX 20

Only to run into that cert issue. (I suppose it's resolvable. I would
like STARTTLS be mandatory for IPv6 sites, but that's me, and contrary
to established practice)

So I made have both an A and AAAA record in DNS, and
made that the only MX record for the domain. Thus far I only have issues
when I have no real ipv6 connectivity, but ipv6 is enabled. Incoming
from the internet, well, can't tell. (Any  bounces from me out there?

I know that neither of these have much to do with the RFC in question.

I've been documenting my experiments with ipv6 on my blog via tag:

Haven't seen a lick of spam via ipv6, which is a plus. Mail over ipv6
gets through in a 90s style (and refreshing) split second because I have
no rbls....

> I'm looking for help answering these questions:
>   *    How are existing IPv6-enabled mail sites actually dealing with
>     missing MX records?
>   *    Are the IPv6-enabled email sites mostly following the
>     recommendations found in RFC 3974?
>   *    How widespread is the use of implicit MX with AAAA records? That
>     is, how prevalent are email sites that do not have MX records
>     but do have AAAA records?
>   *    How big is the existing IPv6-enabled email world?
>   *    What problems, if any, has been experienced by following RFC
>     3974?
> Also, who else could I send this message to in order to gain
> additional insights?
> Thank you!
>     Tony Hansen
>     "shepherd for 2821bis"
>     tony at

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