Re: Question: UseSTD3ASCIIRules on RHS of IMA

   Informative text doesn't hurt, I guess, but IMAA shouldn't make
   normative statements about this IMHO.

   All application must already know the answer to this problem, as the
   same problem existed before IDNA.  If the RFCs are unclear, that
   should be fixed independently of IMAA.

This is what IDNA says, but I'm not sure it's true.  I doubt most mail
software knows the answer to this problem; I suspect that most MUAs
simply pass the address to the MTA and see what happens, and that most
MTAs simply pass the domain to the resolver and see what happens.

In the absence of an RFC-mandated requirement to validate the domain,
it could be argued that this is the correct thing to do in terms of the
robustness principle, even if the domain name contains characters that
are technically illegal.

However, with IMAs, the MUA has to explicitly invoke IDNA, and it
hence has to choose a value for the UseSTD3ASCIIRules flag.  It isn't
absolutely clear to me what the correct value of this flag is (though
it may be clear to others), and it's highly desirable that IMAA
implementations behave consistently.  I don't see why normative text
must be ruled out.

   -roy