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Re: IPv6

2007-03-31 13:53:14

John C Klensin wrote:

One thing that's IMO worse than bogus bounces are lost bounces.

Frank, this seems to me to be getting out onto the slippery
slope toward inventing new rule and requirements, but that is
just my personal opinion.

Not necessarily, you already have similar considerations in 2.3.8
derived from 1123 5.3.7.

You could add a note that MTAs accepting "IPv6 mail" and forwarding
it as "IPv4" are considered as gateways if the reverse-path cannot
be reached via IPv4.  Then they MAY either the rewrite reverse-path 
to something working in an IPv4 environment, or they MAY reject it.

It's probably not yet obvious that this is a *gateway* scenario.

propose something specific for people to evaluate, rather than
just pointing out issues.

1123 5.3.7D offers (about RFC 822 addresses, your 3.7.4):

5.3.7D: they must be effective and useful for sending replies.
= 3.7.4: and MUST be effective and useful for sending replies.

I'm not sure what 1123 5.3.7F means for this issue, 3.7.5 is

| If the foreign environment has no equivalent concept, the
| gateway must select and use a best approximation, with the
| message originator's address as the default of last resort.

Assuming that "IPv6 only" is a kind of "foreign environment"
for IPv4 mailers that's not good enough if the "last resort"
is still "IPv6 only".

How about a more radical approach, just forbid "IPv6 only"
for the moment somewhere in section 5 ?  "IPv6 only" is IMO
completely against the spirit of "if it can't receive mail
it has no business to send mail".