Punycode & IMA/EAI

Shawn Steele Shawn.Steele at microsoft.com
Tue May 20 01:02:16 CEST 2008

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).

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.

- Shawn

-----Original Message-----
From: John C Klensin [mailto:klensin at jck.com]
Sent: Monday, May 19, 2008 3:35 PM
To: Shawn Steele; idna-update at alvestrand.no
Subject: RE: Punycode & IMA/EAI

--On Thursday, 15 May, 2008 14:36 -0700 Shawn Steele
<Shawn.Steele at microsoft.com> wrote:

> That's kind of what I meant. The EAI specifies UTF-8 for the
> domain part, not punycode, so a mail server can't deliver the
> mail unless they know how to do the Punycode conversion (or
> their DNS API does it for them).  Therefore requiring unknown
> A-names resolve might enable a URL, but mail will still break.
> If I own the domain that won't help me then.

Actually, no.   Since an A-label is a valid LDH name, it is
valid even under 2821.  Put differently,
ASCII-string at A-label.domain.example is perfectly valid until
2821/2822 and does not,  by itself, require any EAI handling at
all.  Of course, an EAI-competent UA is required to be
IDNA-compliant, so the usual display issues that we have
discussed immediately appear,  but that is no different either.


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