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

2020-09-28 18:35:56
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.

John Levine, johnl(_at_)taugh(_dot_)com, Taughannock Networks, Trumansburg NY
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