IPv6 isn't SMTP

rwebb at ropeguru.com rwebb at ropeguru.com
Wed Mar 26 13:05:52 UTC 2014

On Wed, 26 Mar 2014 07:45:06 -0500
  Daniel Taylor <dtaylor at vocalabs.com> wrote:
> On 03/25/2014 11:18 PM, John Levine wrote:
>>> 3.  Arguing about IPv6 in the context of requirements upon SMTP 
>>>connections is playing that uncomfortable game with
>>> one�s own combat boots.  And not particularly productive.
>> If you can figure out how to do effective spam filtering without
>> looking at the IP addresses from which mail arrives, you will be in 
>> position to make a whole lot of money.
>> But, as always, I'm not holding my breath.
>> R's,
>> John
>> PS: Note the word "effective".
> You look at the IP, and verify forward and reverse DNS.
> IPv6 doesn't make this any harder a problem than IPv4, it just means 
>that we're going to *have* to reject mail that comes in from IPv6 
>addresses that don't have clean DNS.
> -- 
> Daniel Taylor          VP Operations            Vocal Laboratories, 
> dtaylor at vocalabs.com   http://www.vocalabs.com/ 
>           (612)235-5711

Actually, with all the discussion about ipv6 not having rDNS, in most 
cases, would that not make things easier? So those that want to run 
email servers SHOULD be on ISP's that allow for rDNS configuration for 
IPv6. There should be some vetting in the process by the ISP, maybe, 
before allowing this. So in essence, if you are a legitimate email 
host, you will have rDNS configured on IPv6 for your server. Again, as 
others have stated, rDNS should NOT be the only deciding factor in 
whether or not an email is legit. No rDNS, or havinf rDNS, should have 
some weight assigned to it for the overall evaluation of the sender.


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