Broadband Tech > IPv6 > Sending emails over Ipv6

Sending emails over Ipv6

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?

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]

reply to probuddha

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

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?

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

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.

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!

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.

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

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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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?