Re: [ietf-smtp] EHLO domain validation requirement in RFC 5321

Keith Moore <> Mon, 28 September 2020 22:27 UTC

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To: John Levine <>,
References: <20200928221602.046CE22A35B3@ary.qy>
From: Keith Moore <>
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Date: Mon, 28 Sep 2020 18:26:57 -0400
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Subject: Re: [ietf-smtp] EHLO domain validation requirement in RFC 5321
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On 9/28/20 6:16 PM, John Levine wrote:

> You appear to be saying there will be mail systems that need to send
> mail to IPv4 systems, but will not have an IPv4 mail server so the
> recipients can't reply to them.  Really?

No, I'm saying that when IPv4 starts going away, there will be more and 
more systems needing to send mail via NAT to such that client and server 
ends of the connection have different address types.

(There are already some IPv6 only ISPs and I expect this will become 
more viable over time.   Should they have to set up IPv4 tunnels or ALGs 
for their "legitimate" customers so those customers can still send email 
to IPv4 servers?)