Re: idna folding (was Re: idna-bis and '゜')

Erik van der Poel erikv at
Tue Dec 18 03:38:14 CET 2007

Hi Vint,

Yes, I've been rather focussed on the web, sorry about that. I haven't
been involved in the email i18n discussions, but let's consider it.
It's my understanding that when an SMTP server supports the UTF-8
option, the client may send the recipient's email address in UTF-8 in
the envelope. Since SMTP servers typically do not allow any user to
edit these addresses upon receipt, they may try to verify them
automatically. Perhaps the server would want to convert the UTF-8 host
name to Punycode, to verify it. This may be a situation where it would
first apply case mappings and NFKC a la IDNA2003 (or some newer spec).
Or maybe the SMTP UTF-8 spec explicitly forbids that or specifies
something else, I don't know.

In any case, it would be great if all such "automatic" conversions
(i.e. without end-user editing) were done according to a single
mapping spec, whether the app is a web browser, email, or whatever.
Does this seem like a good idea?


On Dec 17, 2007 3:47 PM, Vint Cerf <vint at> wrote:
> Please keep in mind other than browser-based applications when analyzing these issues. The net is more than the web. V
> ----- Original Message -----
> From: idna-update-bounces at <idna-update-bounces at>
> To: Patrik Fältström <patrik at>
> Cc: Thomas Roessler <roessler at>; Mark Davis <mark.davis at>; Harald Tveit Alvestrand <harald at>; John C Klensin <klensin at>; Paul Hoffman <phoffman at>; idna-update at <idna-update at>; Martin Duerst <duerst at>
> Sent: Mon Dec 17 15:36:50 2007
> Subject: Re: idna folding (was Re: idna-bis and '゜')
> I see. This sounds like the mappings that are performed in the UI (as
> opposed to the mappings that the browsers perform for <a href="...">
> and <img src="...">). I do see the need for interoperability at the UI
> level too. So we might have three different levels in the documents:
> (1) IDNA200X protocol spec (no mappings)
> (2) mapping spec (where user is not editing the host name;
> language-independent; e.g. HTML in search engines)
> (3) UI recommendations (where user is editing the host name;
> potentially language-dependent; e.g. user typing host name into
> browser)
> It would be nice if we only had one spec at level (1), and only one
> spec at level (2).
> We might have multiple documents at level (3), for various languages, apps, etc.
> Erik
> On Dec 17, 2007 3:02 PM, Patrik Fältström <patrik at> wrote:
> >
> > On 17 dec 2007, at 17.30, Erik van der Poel wrote:
> >
> > > Would you please confirm whether you are talking about registration or
> > > resolution here?
> >
> > I have got requests from browser programmers whether it is possible
> > for them to know what equivalences the registries have used at time of
> > registration. So that the browser when accepting written input (on a
> > keyboard) can do similar mappings etc that is happening at time of
> > registration. Context dependent mapping. If nothing else to possibly
> > minimize phishing etc while still ensuring no false positives.
> >
> > I.e more and more requests I have got regarding mapping at time of
> > lookup is to know how to ensure the mapping at resolution is the same/
> > similar as mapping at time of registration.
> >
> >     Patrik
> >
> >
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