Re: Last Call: draft-klensin-rfc2821bis

Tony Finch wrote:
> On Sat, 29 Mar 2008, John Levine wrote:
>> Getting rid of the AAAA fallback flips the default to be in line with
>> reality -- most hosts don't want to receive mail directly, so if
>> you're one of the minority that actually does, you affirmatively
>> publish an MX to say so.
> 
> I agree that this is the right thing to do in an ideal world.
> 
> However there's a lot of old running code out there that implements the
> AAAA fallback. Is IPv6 still enough of a toy that the stability of its
> specifications doesn't matter?

You could make the same kind of argument in the other direction: Is IPv6 
still enough of a toy that we shouldn't maintain the specifications for 
applications that use it, updating them when there's a good reason to do so?

I'm not worried about running code that implements the AAAA fallback, 
because I don't think that this change breaks anything.  If domains were 
already relying on just an AAAA record to tell other domains how to send 
  mail to them, I'd be concerned about backward compatibility.  But 
that's  not the case.
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