On Wed, Jun 04, 2014 at 12:45:40PM -0400, Wietse Venema wrote:
> > As far as I can tell the xn-- mumble is never used outside the DNS lookups,
> > neither in the RFCs nor in practice. The EAI RFCs say to use the xn-- form
> > for MX lookups, to use an ASCII domain name for the EHLO argument, and
> > otherwise don't discuss xn--.
Lack of discussion simply means that the relevant discussion is in
other documents. For example, in X.509 subjectAltName DNS, the
domain name needs to be in ASCII form.
My impression is that UTF-8 domain names are are an MUA display
format issue. All domain names "on the wire", including in email
headers should be in ASCII form, to be displayed by MUAs as UTF-8
when appropriate. I've not checked whose responsibility it is to
perform the conversion from what the user types to the A-label form
of the domain. Ideally, this is done by the MUA. Potentially this
could also be done by an MSA (before applying DKIM signing, ...).
Perhaps UTF-8 domains are allowed in headers (a bad idea IMHO, even
if bless by the RFC), but they should be converted to A-labels as
quickly as possible. UTF-8 text may then appear in the address
localpart, and in "phrases" (Full Name, ...). One might also expect
UTF-8 in some MIME headers (obviating RFC 2231 encoding of MIME
attribute values), however when the payload is a domain it should
I think be in A-label (wire) form.
Thus for example, in DKIM the "d=" attribute should be ASCII, ..
Finally, I still view EAI RFCs with a healthy dose of skepticism.
Where good judgement runs contrary to the RFCs, I'll go with good
judgement.
--
Viktor.
