John;
Third, while it would certainly make global interoperability easier,
there is no way to prevent people from deciding to use local characters,
and maybe even local codings, in local environments. They will do it.
That something is technically possible does not mean it useful.
In this case of localized (not internationalization at all) email
addresses, it is not useful and will not be used widely to be
ignored safely.
They will believe (probably correctly) that they have good reasons for
doing it. Our choices are between
* Finding a rational, plausible, global way to let them
do it while still preserving global interoperability or
Mails with localized addresses do not interoperate globally
just beause they use localized addresses that that is a
meaningless goal.
Fourth, there was, and is, a case to be made that internationalization
of domain names is unnecessary and dumb
Right. Localized domain names are not useful and not used at all,
at least in Japan. Maybe, there are some names registered, as
protection purposes, but none are used.
Even if there is a few countries where such domain names are used,
it proves that the issue is purely local with no international
issues and no global interoperability is necessary.
You can argue that localized domain names was useful for registries
and registareres, as names registered for protection purposes
increased their revenues, though I guess, in Japan, that
outcome of advertisement fee on various media exceeded income
of registration.
But, even such argument is not applicable to email names.
Masataka Ohta