In other words, this was a major standards screwup and we get to deal with the consequences :(

All right, since I'm hardly likely to have time to deal with it anyway, we'll just say that email isn't going to handle unicode domain names until *someone* figures out how to do this right.  And it sounds like that may be never.  Because saying that "users that want to make requests to IDNA domains should be responsible for the encoding themselves" is, really, a *complete* non-starter from any perspective I can think of, and has its own security issues.  If UTF46 does not do the job, we are just out of luck and the users will pay the price.