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

2008-04-15 13:40:24

Arnt Gulbrandsen wrote:

sm(_at_)resistor(_dot_)net writes:
Not necessarily. That host may apply a different policy for mail coming through the other MX hosts. Otherwise, it would cause backscatter. BTW, the problem may be applicable to IPv4 as well.

Oh wait, I misunderstood what you're saying. And you probably misunderstood me. doesn't have an IPv6 MX, so the only way to deliver mail to it is to open an IPv4 SMTP connection.

Suppose I have only an IPv6 address and want to send John mail (sorry to pick on you, John). I open an IPv6 connection to my ISP's smarthost and send some mail from my address to a address. My ISP's smarthost has an IPv4 address, so it opens an IPv4 connection to the best reachable MX for The connection from my ISP's smarthost to the MX is what I pasted, and where the problem shows up.

Exactly. You SHOULD NOT expect IPv6 feedback behavior to be automatic or reliable, especially from a IPv6 Only client to dual stack smarthost. It will only work if replies are going back thru the same compatible host routing which is generally not the case under a smarthost.

And the text I think should be there would be a sentence like this in sections "Note that the reverse-path may be reachable only via IPv6, even if the SMTP connection uses IPv4", possibly with some emphasis to point out that perfectly valid 2821 code/configurations don't support this. would need similar language for "forward-path".


And this is why I was proposing the text that if a IPv6 aware client was sending to mail out to a IPv4 client (because it used a IPv4 socket connection), it SHOULD NOT make any presumption that the receiver would be able to *communicate* back (in sending a bounce or user reply) using IPv6. If it doesn't provide a compatible IPv4 layer, then its should expect lost of mail.

Unless you have a middle man or proxie handling all the outbound and inbound for you, you will need to have a dual stack smtp system for direct contacts from IPv4 systems.


Hector Santos, CTO