It appears that John C Klensin <john-ietf(_at_)jck(_dot_)com> said:
It would certainly be appropriate to either revise the spec or,
better from my point of view, create a short applicability
statement that explains the reasoning behind the SHOULD and the
circumstances under which it would be sensible to ignore it. ...
The thing that sometimes gets lost in "let's make the spec
conform to what implementations are doing" discussions in this
area is that there is an assumption behind the whole collection
of SMTPUTF8 specs, namely that the world really wanted non-ASCII
addressing and header field values. ...
This may seem like splitting hairs but there is a difference between
header fields that users see and fields that they don't. Message-IDs
are still generally ASCII in EAI messages, and I don't see any
benefit from making the domain names in trace headers U-labels rather
than A-labels.
I'm not getting any pushback on Return-Path which really does need
to be UTF-8 is it's an EAI address. I think the few MTAs that put
a FOR clause in the Received header put EAI addresses there, too.
R's,
John
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