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probuddha

join:2010-08-10

Sending emails over Ipv6

Hi

I would like to know how I can send emails over an IPv6 address.

Our hosting provides Ipv6 addresses and our mail server is already pointed to an A record (Ipv4) as well as an AAAA record (IPv6)

While doing some rounds of testing, I found that one of the emails that landed in Gmail was sent from the Ip6 address instead of the Ip4 one, but this doesn't happen always. And in Yahoo and Hotmail, it's the IP4 that's always the sending IP

The primary NS of our domain is pointed to the IP6 address.

I would like to know, how I can always make the outgoing emails originate from the Ip6 address.

Would it help if I delete the A record for our mail server and keep the AAAA record live (sorry if it's a dumb question)

Kindly advise

Thanks



justbits
More fiber than ATT can handle
Premium
join:2003-01-08
Chicago, IL
Reviews:
·Comcast Business..

1 edit

2 recommendations

Sorry... I had posted a response about DNS records... looks like you have that configured correctly. Deleted that.

The mail transfer agent (postfix, exim, sendmail, etc) will choose which mail server to use based on which MX is the highest priority. If the highest priority doesn't have an IPv6 address, it won't use it. Look at hotmail.com's MX records. I don't see any IPv6 addresses in their MX hosts. Same thing with yahoo.com.

As to why the MTA chooses Google IPv4 sometimes and Google IPv6 sometimes, that's a tough one to answer. Maybe the IPv6 DNS lookups are taking too long, so it uses the IPv4 address instead? Maybe the DNS response "load balances" the A and AAAA records in a round robin way and the MTA is affected by that?


seaprobe

join:2006-07-16
Sunnyvale, CA

2 recommendations

reply to probuddha

It may also be related to the "Happy Eyeballs" RFC for IPv6:

This is non-deterministic in that is simply chooses the "fastest" transport in a dynamic way. As long as both transports are working well, one will see an apparently random mix.

Quoting briefly:

An application that uses a Happy Eyeballs algorithm checks both IPv4 and IPv6 connectivity (with a preference for IPv6) and uses the first connection that is returned. The addresses are often chosen from the DNS with a round-robin algorithm.[3] Implementations of Happy Eyeballs stacks exist in Google's Chrome web browser, Firefox version 13, and Mac OS X Lion[4] (although Lion uses the fastest connection, rather than preferring IPv6).[5] Happy Eyeball testing was part of World IPv6 Day in 2011.[6]



leibold
Premium,MVM
join:2002-07-09
Sunnyvale, CA
kudos:10
Reviews:
·SONIC.NET

said by seaprobe:

It may also be related to the "Happy Eyeballs" RFC for IPv6:

Strange title for an RFC, but it is for real and since RFC 6555 is on the standards track we may see this kind of behavior from more and more applications (it is more likely to be implemented in an application then in the OS kernel).
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34764170

join:2007-09-06
Etobicoke, ON
reply to probuddha

said by probuddha:

Hi

I would like to know how I can send emails over an IPv6 address.

What e-mail server software is being utilized?

probuddha

join:2010-08-10

We're using QMAIL on the server

Would it help if I disallow mail traffic only on the IPv4 address, since the mail server is pointing to both an A as well as an AAAA record, if I block traffic through IP4, would it automatically take the IP6 in consideration or is this totally not possible

Thanks



graysonf
Premium,MVM
join:1999-07-16
Fort Lauderdale, FL
kudos:2

If you disable IPv4, what do you think will happen when your mail server on an IPv6 address tries to relay mail to another that is not IPv6 capable?


probuddha

join:2010-08-10

Right...my concern as well.

I've seen Google supporting IP6 addresses but haven't seen Yahoo and Hotmail support it.

So in that case the emails won't be delivered to Yahoo and Hotmail



graysonf
Premium,MVM
join:1999-07-16
Fort Lauderdale, FL
kudos:2

I think you are underestimating the impact.

You have no way of knowing where you will be sending mail to in the future, and of those destinations, which are IPv6 capable or not.

The best you can do, and the most sensible approach, is to configure both IPv6 and IPv4 addresses on your mail server and in your DNS A and MX records. Then if you wish and can, set your mail server to prefer IPv6 over IPv4 for outbound mail.

But in the end, it will always be the recipient domains that dictate how mail is transported into their servers, and that is not within your control.


probuddha

join:2010-08-10

Hi graysonf

Thanks a lot for your reply

I totally understand and agree to the concern you've raised...we'll be sending emails to a lot of other email servers other than that of Google, Yahoo and hotmail

This is how our DNS records are laid out now

The mail server and the A records and in fact all the other records are set on both an A as well as an AAAA address...

Now if I understand your solution properly, I need to set up another mail server with an IP6 address and set it's priority higher than the existing one that is using an IP4 address.

Is that what you're suggesting, thanks!



graysonf
Premium,MVM
join:1999-07-16
Fort Lauderdale, FL
kudos:2

No, and I don't know how you got the idea that I suggested that.

You seem to be confusing outgoing mail and incoming mail, and how and where DNS is involved with both.


probuddha

join:2010-08-10

Ahh...sorry..I am a novice at all this and just trying to learn



leibold
Premium,MVM
join:2002-07-09
Sunnyvale, CA
kudos:10
Reviews:
·SONIC.NET

The MX records for your domain name determine the names of your incoming email servers (whether or not they also handle outgoing email is completely irrelevant) as well as the priority that determines in which order a sender should be trying them.

The A and AAAA records for those email server names provide the IPv4 and IPv6 addresses that are actually used to establish the connection to the email server. In addition the A and AAAA records are used as a fallback if a domain name doesn't have any MX records associated with it.

The same applies in the outgoing direction with the important difference being that it is the MX, A and AAAA records of the destination domain that matter instead of your own DNS records.
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IamGimli

join:2004-02-28
Canada
kudos:2

1 recommendation

reply to probuddha

My question would be: why do you care whether emails sent from your mail servers are sent using IPv6 or IPv4? Shouldn't your concern be whether they make it to their destination or not?

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