Punycode & IMA/EAI

John C Klensin klensin at jck.com
Tue May 20 10:52:41 CEST 2008

--On Monday, 19 May, 2008 16:02 -0700 Shawn Steele
<Shawn.Steele at microsoft.com> wrote:

> A-labels are valid, but the draft specifies UTF-8 for
> international addresses.  So I'd assume it would be uncommon
> to find an A-label in an EAI name, unless something odd
> happened.  (Like the user entered the punycode name by hand,
> or it was used in an alt-addr fallback).

Hard to predict.  If I have an IDN mail domain that contains
characters for which I don't have an IME (or don't know how to
use it), and happen to have the A-label(s) handy, I might prefer
to use them.  That, of course, pretty much assumes an ASCII
local-part with a partially or completely non-ASCII domain.  I'd
expect that to be an uncommon case, but am not taking bets.

> The point is that since they are normally manipulated in
> Unicode, the application MUST know how to do the punycode
> conversion.  If it can't, the forward looking behavior isn't
> helpful.


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