Re: Last Call: draft-klensin-rfc2821bis

>> and the dummy SMTP server works, but it consumes resources on the  
>> host and eats bandwidth on the network.  having a way to say "don't  
>> send this host any mail" in DNS seems like a useful thing.  and we  
>> simply don't need the fallback to AAAA because we don't have the  
>> backward compatibility issue that we had when MX records were  
>> introduced.
> 
> Not sanctioning IPv6 AAAA records as an MX fall-back avoids the  
> undesired traffic now caused by SMTP spoofing of A records.  MX  
> records might then be seen as an opt-in mechanism from the perspective  
> of IPv6, since opt-out mechanism are onerous for those not wishing to  
> participate.  While Bill and others expressed concerns of being tied  
> to DNS, whatever replaces DNS must also offer separate service and IP  
> address resolution mechanisms.

there are lots of cases where I'd share the concern that DNS gets out of 
sync with reality.  but having this information in DNS doesn't bother me 
in this case because the servers to which incoming mail messages to 
user@example.com are supposed to be sent, are a property of the 
example.com domain, far more than a property of any host.  it makes 
sense to put information about a domain in DNS (or whatever might 
someday replace DNS).

Keith
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