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

John R Levine <johnl@taugh.com> Mon, 28 September 2020 23:35 UTC

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Date: 28 Sep 2020 19:35:42 -0400
Message-ID: <ab8886ec-79b1-a89c-da38-dfe5a6e681@taugh.com>
From: "John R Levine" <johnl@taugh.com>
To: "Mark Andrews" <marka@isc.org>
Cc: ietf-smtp@ietf.org
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Subject: Re: [ietf-smtp] EHLO domain validation requirement in RFC 5321
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> Actually I expect there will be systems where just 25/<ipv4-address> is
> statically NAT46’d to a 25/<IPv6-address> and all the outbound traffic goes
> back through the NAT64 with no linkage to the IPv4 address except for those
> established by the inbound connections.

Hmmn.  I suppose that if I wanted to set up a mail system to maximize the 
chance that my mail would fall afoul of well established anti-abuse 
metrics and get thrown on the floor, that'd be a good plan.

On the other hand, if I were running a mostly v6 network and wanted a mail 
path for a few legacy v4 users, I would set up a gateway on a dual stacked 
host with static IPv4 and IPv6 addresses, publish its v4 address as a 
secondary MX for my v6-only mail systems, and use it to pass mail both 
ways.

Regards,
John Levine, johnl@taugh.com, Taughannock Networks, Trumansburg NY
Please consider the environment before reading this e-mail. https://jl.ly