I bought xn--mn8h9e.ws a couple years ago just for fun. I think it's fun to own an emoji domain, but what I can say definitely say is that it's still a bad idea to own one if you want to get emails to it. Popular thick email clients still struggle with utf8 domains and I've fiddled around with several email providers that just have complete failures trying to send as well. I tried pasting the email address in a bunch…
According to the IETF standard for IDNA it is invalid. https://itp.cdn.icann.org/en/files/security-and-stability-ad... https://www.icann.org/en/system/files/files/idn-emojis-domai...
Even if emoji was invalid, unicode in general is valid in domain names, and should be converted to punycode. Local domains exist too.
It’s not the email client’s job to decide whether a domain is valid, it’s DNS’.