Punycode & IMA/EAI

John C Klensin klensin at jck.com
Tue May 20 00:35:00 CEST 2008

--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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