That's the spec, for sure! The domains are converted to punycode, but the usernames? I have no idea what happens to them. My tests showed some providers deliver

That's the spec, for sure! The domains are converted to punycode, but the usernames? I have no idea what happens to them. My tests showed some providers delivered them, some didn't. I'm sure there are a bunch of people out there using accented characters and CJK etc in their usernames and wondering why it's not going so well...