Re: [idn] How should labels be encoded?

["Adam M. Costello" <amc@cs.berkeley.edu>]

David Hopwood <david.hopwood@zetnet.co.uk> wrote:

> > The SOA record contains one that is an e-mail address.
>
> Since the local part of an email address is internationalizable text,
> and is subject to exactly the same compatibility and normalization
> considerations as domain names, it should use the same encoding as
> domain names, IMHO.

This working group is not the place to decide how to internationalize
email address local-parts.  Local-parts do not have exactly the same
compatibility and normalization considerations as domain names: they
may contain non-LDH ASCII characters, they may be case-sensitive, and
they may be structured using separators other than "." (for example,
owner-FOO and FOO-request and FOO+TAG are common constructions that have
particular relationships to FOO).  I once tried to start discussing this
issue and was told (correctly) that it's off-topic for this working
group.

> This does make clear, however, that it is not correct for a general
> purpose resolver interface to reject non-LDH ASCII characters;
> instead, it should pass through such characters (if no non-LDH
> characters are used in that domain, the query will simply fail).

You seem to be confusing queries and responses, or domain names and
resource records.  Currently, all domain names (which are the things
that appear in queries) are advised to use the preferred name syntax
(LDH characters in labels).  The resource records (the things that
appear in responses, like SOA and SRV data) already contain non-LDH
characters, and of course they are not rejected for that.  Some resource
records contain domain names (like CNAME and PTR) but some contain
other things.  The mailbox field of the SOA record, even though it is
formatted as a sequence of labels, is not a domain name and is not
expected to conform to the preferred name syntax (although after you
chop off the first label, the result is a domain name and is expected to
conform).  I gather than the same is true of the SRV record.

AMC