Re: [Emailcore] Ticket #50: Use of top level domains in SMTP

John Levine <johnl@taugh.com> Fri, 23 July 2021 22:37 UTC

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Date: Fri, 23 Jul 2021 18:37:19 -0400
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From: John Levine <johnl@taugh.com>
To: emailcore@ietf.org
Cc: dcrocker@bbiw.net
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Subject: Re: [Emailcore] Ticket #50: Use of top level domains in SMTP
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It appears that Dave Crocker  <dcrocker@bbiw.net> said:
>On 7/23/2021 7:38 AM, Alexey Melnikov wrote:
>> I believe there was rough agreement in the past that use of top level 
>> domains is going to cause interop problems, as depending on context they 
>> might not be distinguishable from local hostnames. If people agree, I 
>> think the Applicability Statement draft should talk briefly about this.
>
>
>Yes, as long as the language makes clear that the conflict is between an 
>enhanced, standardized bit of functionality, with local, 
>non-standardized functionality.

Ever since Paul Hoffman and I published RFC 7085 in 2013 I've been doing surveys of what's
in the top level of TLDs.  There are currently 17 ccTLDs that have MX records at the top,
For most of them, even if you can persuade your MUA to send them mail, it doesn't actually
work.  GT. and TT. point their MX at Google, which I think is a surprise to Google.

So I agree, if you want to interoperate, the domain in an address has to have at least
two components.  I suppose Dave's point is correct, but that applies to just about anything
in any IETF standard.

R's,
John