Subject: [v6ops] IPv6-only SMTP delivery?

From: Ted Lemon <[email-masked]>
Date: Fri, 8 Jul 2011 17:02:04 -0400

Maybe this is a dumb question, but it occurred to me today to check to see if it's possible to receive mail from IPv6-enabled servers if your MX record points to a name with a valid AAAA but no A record.   Although I had no trouble delivering the mail to my mail server using a telnet session over IPv6, when I tried to send mail the usual way it bounced.   One MTA gave me this:

<[email-masked]>: host other.example.com[10.20.30.40] said: 550 MX
 record points to an invalid IP for domain:my.example.com - usmtp (in reply to
 RCPT TO command)

When I tried to send the mail from gmail, I got no bounce, but the mail hasn't arrived after several hours, so I think it's safe to assume it's not going to.

I'd never thought to look into this issue before, so I suppose it's possible that I'm missing some RFC that says SMTP is only supported for now on dual-stack and v4-only devices, not on v6-only devices, but it seems unlikely to me.

So what's going on here?   Are people disabling delivery over IPv6 for operational reasons, or are the implementations broken? Is this something we ought to be talking about?

---

From: Keith Moore <[email-masked]>
Date: Fri, 8 Jul 2011 19:15:14 -0400

> So what's going on here?   Are people disabling delivery over IPv6 for operational reasons, or are the implementations broken? Is this something we ought to be talking about?

There's no assurance that any MTA that is handling your outbound mail has IPv6 capability, and no requirement that they provide such capability.

Practically speaking, you're going to need at least one IPv4-capable MX for your domain for the foreseeable future.

Keith

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From: Erik Kline <[email-masked]>
Date: Sat, 9 Jul 2011 09:11:07 +0900

> When I tried to send the mail from gmail, I got no bounce, but the mail hasn't arrived after several hours, so I think it's safe to assume it's not going to.

Gmail does not yet have IPv6-capable SMTP in nor out.  It only has
AAAAs for the web frontend as well as POP and IMAP.

---

From: "Brzozowski, John" <[email-masked]>
Date: Sat, 9 Jul 2011 01:19:57 +0000

Ted,

I think there is an assumption here that mail sent to an SMTP server for
delivery could be IPv6 only, however, the transmission to the destination
will likely be dual stack for some time and more than likely default to
IPv4 only.  We have recently enabled as part of our trials SMTP servers
for Comcast trial users to send mail through, however when delivering the
same there is an assumption that the server is dual stack.

We do not yet have inbound mail receipt enabled over IPv6.  Spam
mitigation for IPv6 does not appear to ready just yet.

To answer your question, the choice at this time appears to be operational.

FWIW - when mail is sent via mail servers over IPv6 the message header on
the receiving end will in fact report the source IPv6 address.  This is at
least what we have observed.

John
=========================================
John Jason Brzozowski
Comcast Cable
e) mailto:[email-masked]
o) 609-377-6594
m) 484-962-0060
w) http://www.comcast6.net
=========================================

On 7/8/11 5:02 PM, "Ted Lemon" <[email-masked]> wrote:

>Maybe this is a dumb question, but it occurred to me today to check to
>see if it's possible to receive mail from IPv6-enabled servers if your MX
>record points to a name with a valid AAAA but no A record.   Although I
>had no trouble delivering the mail to my mail server using a telnet
>session over IPv6, when I tried to send mail the usual way it bounced.
>One MTA gave me this:
>
>When I tried to send the mail from gmail, I got no bounce, but the mail
>hasn't arrived after several hours, so I think it's safe to assume it's
>not going to.
>
>I'd never thought to look into this issue before, so I suppose it's
>possible that I'm missing some RFC that says SMTP is only supported for
>now on dual-stack and v4-only devices, not on v6-only devices, but it
>seems unlikely to me.
>
>So what's going on here?   Are people disabling delivery over IPv6 for
>operational reasons, or are the implementations broken? Is this something
>we ought to be talking about?
>_______________________________________________
>v6ops mailing list
>[email-masked]
>https://www.ietf.org/mailman/listinfo/v6ops

---

From: Bob Van Zant <[email-masked]>
Date: Fri, 8 Jul 2011 19:16:46 -0700

I have an IPv6 email reflector setup here for anyone that wants to
goof around and see what at least one other MX on the Internet sees.

[email-masked]

I've had my email domains accepting email over v6 for about a year
now. Spam filtering with only content filtering (no IP reputation) has
been working out well. IPv6 email as a percentage of total email is
paltry and spam as a percentage of that is way below what I see on
IPv4. I say flip a AAAA on one of your less important MX records and
start experimenting.

-Bob

---

From: Ted Lemon <[email-masked]>
Date: Fri, 8 Jul 2011 22:51:19 -0400

> Practically speaking, you're going to need at least one IPv4-capable MX for your domain for the foreseeable future.

That's not the question I was asking.   Erik's response is more on point, because he's speaking to his own company's operations.   The real question I'm asking is, is this something we ought to be talking about?

---

From: Ted Lemon <[email-masked]>
Date: Fri, 8 Jul 2011 22:57:20 -0400

> mitigation for IPv6 does not appear to ready just yet.

This is exactly what I'm interested in.   It makes sense that you wouldn't enable inbound SMTP for precisely this reason.   But why not enable it for outbound?   I think Erik's answer makes sense, although it's a bit unfortunate, but if you have the operational capability to make an outbound IPv6 SMTP connection, is there any reason why you'd deliberately disable it?

---

From: "Brzozowski, John" <[email-masked]>
Date: Sat, 9 Jul 2011 03:06:01 +0000

We are looking at outbound, the work right now is to ensure the mail
platform is stable and scales, etc.  Once all of this is ready one could
simply add AAAAs for the SMTP servers.  The issue of connectivity may come
into play specifically if mail clients think they have some form of IPv6
but truly do not or the same is poor.  I suspect SMTP would be more
forgiving unlike end users visiting web sites (HTTP).

John

On 7/8/11 10:57 PM, "Ted Lemon" <[email-masked]> wrote:

>This is exactly what I'm interested in.   It makes sense that you
>wouldn't enable inbound SMTP for precisely this reason.   But why not
>enable it for outbound?   I think Erik's answer makes sense, although
>it's a bit unfortunate, but if you have the operational capability to
>make an outbound IPv6 SMTP connection, is there any reason why you'd
>deliberately disable it?
>

---

From: Ted Lemon <[email-masked]>
Date: Fri, 8 Jul 2011 23:33:11 -0400

On Jul 8, 2011, at 11:06 PM, Brzozowski, John wrote:
> The issue of connectivity may come

Certainly *submitting* mail over SMTP when you have a non-working IPv6 prefix would introduce a delivery delay, but as long as the MUA tries v4 as well as v6, the end-user isn't likely to notice it.   But for outbound SMTP, it's really not a problem.   Any MTA worth its salt already understands how to try alternatives, and SMTP is a store-and-forward protocol, so instant delivery isn't particularly expected.

---

From: Gert Doering <[email-masked]>
Date: Sat, 9 Jul 2011 11:00:22 +0200

Hi,

On Fri, Jul 08, 2011 at 05:02:04PM -0400, Ted Lemon wrote:
> Maybe this is a dumb question, but it occurred to me today to
> check to see if it's possible to receive mail from IPv6-enabled
> servers if your MX record points to a name with a valid AAAA but
> no A record.   

No problem, *if* the client side software supports it.  For demonstration
purpose, I've used "[email-masked]" before, and that
resolves to:

$ host v6only.greenie.net
v6only.greenie.net has IPv6 address 2001:608:0:1007:a00:20ff:fefe:4bd2
v6only.greenie.net mail is handled by 5 v6only.greenie.net.

> Although I had no trouble delivering the mail to my
> mail server using a telnet session over IPv6, when I tried to send
> mail the usual way it bounced.   One MTA gave me this:
> 

Sounds like a client MTA that has no IPv6 support compiled in...

> When I tried to send the mail from gmail, I got no bounce, but
> the mail hasn't arrived after several hours, so I think it's safe
> to assume it's not going to.

As far as I understand, gmail has no v6 yet on the "mail side of things".

> I'd never thought to look into this issue before, so I suppose
> it's possible that I'm missing some RFC that says SMTP is only
> supported for now on dual-stack and v4-only devices, not on v6-only
> devices, but it seems unlikely to me.

If you have a single-stack v4 client trying to deliever to a single-stack
v6-only server, it will fail.  Nothing new here.

Which is why I run my production mail server dual-stacked, and I receive
quite a lot of e-mail over v6 transport (so it works) - and all the
legacy hosts can still send it over v4.

> So what's going on here?   Are people disabling delivery over
> IPv6 for operational reasons, or are the implementations broken?
> Is this something we ought to be talking about?

I've been told that IPv6 is not available everywhere yet...

Gert Doering
        -- NetMaster
-- 
did you enable IPv6 on something today...?

SpaceNet AG                        Vorstand: Sebastian v. Bomhard
Joseph-Dollinger-Bogen 14          Aufsichtsratsvors.: A. Grundner-Culemann
D-80807 Muenchen                   HRB: 136055 (AG Muenchen)
Tel: +49 (89) 32356-444            USt-IdNr.: DE813185279

---

From: SM <[email-masked]>
Date: Sat, 09 Jul 2011 03:36:49 -0700

Hi Ted,
At 14:02 08-07-2011, Ted Lemon wrote:
>Maybe this is a dumb question, but it occurred to me today to check 
>to see if it's possible to receive mail from IPv6-enabled servers if 
>your MX record points to a name with a valid AAAA but no A 
>record.   Although I had no trouble delivering the mail to my mail 
>server using a telnet session over IPv6, when I tried to send mail 
>the usual way it bounced.   One MTA gave me this:
>

Some mail filters test for invalid A records.  The test may fail if 
there is a (valid) AAAA record.

>possible that I'm missing some RFC that says SMTP is only supported 
>for now on dual-stack and v4-only devices, not on v6-only devices, 
>but it seems unlikely to me.

Mail relaying over SMTP will fail if there isn't any path between the 
IPv6 and IPv4 islands.

>So what's going on here?   Are people disabling delivery over IPv6 
>for operational reasons, or are the implementations broken? Is this 
>something we ought to be talking about?

The well-known SMTP implementations support IPv6.

Regards,
-sm