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

2008-04-15 15:07:49

Hector Santos <hsantos(_at_)santronics(_dot_)com> wrote:

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 loss of mail.

   (I shall try -- really I shall -- to avoid an IPv6 religious war here.)

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.

   My hope has been that an IPv6-only host speaking SMTP to the rest of
the world would:

 - look for an MX RR pointing to an AAAA RR
   - if it finds one, use that AAAA RR
   - if not, look for an MX (explicit or implied) pointing to an A RR
     - if it finds one, pass the email to a friendly relay speaking IPv4
     _ if not, give the usual error

 - advertise an MX RR pointing to an A RR
   (in addition to any pointing to AAAA RRs)

   This strikes me as a more reasonable long-term algorithm than
requiring all mail from an IPv6 user to go through a SMTP server with
both IPv4 and IPv6 connectivity.

   It may be that the consensus here prefers Hector's solution: if so,
I suppose I should shut up. But please think long-term: we want something
that can work today and continue working for 20 years, by which time
IPv4 should be as rare as IPv6 is today.

John Leslie <john(_at_)jlc(_dot_)net>