While we're at it, can we simplify the grammar of an email address? Does anyone really embed comments in their address?

After a quick glance at the standard, I belive email providers like Google who support SMTPUTF8 could support having two email addresses transparently to the user.

According to the standard: "If the message cannot be forwarded because the next-hop system cannot accept the extension, it MUST be rejected or a non-delivery message MUST be generated and sent."

Google could preserve a backup ASCII email for all UTF-8 email addresses, which would be used in the case the recipient doesn't support SMTPUTF8.

Of course, I don't know if Google has plans to support this.

This comment is pretty frightening to me. Email is very often used for "mission critical" purposes, not just for exchanging messages with other users (let alone just "with other users of the top 5 providers"). I know that enabling international characters is important for a whole range of reasons, and that's worth some significant costs. But email infrastructure is emphatically not something where "works most of the time" or even "works 95% of the time" is good enough. I think there really is a need for pretty substantial attention to backward compatibility in this case.

> Almost all email moves between only a handful of companies. Google, Microsoft, Yahoo, Facebook, Apple

That's pretty naive. You need to step outside your comfy bubble.

Out of all the small businesses on the internet, how many of them are still running an email server under someone's desk?

And not to mention, what about all the client-side javascript out there that parses email addresses on web forms? Think about all those throw-away regexes to parse email forms on websites. I've seen a lot of them break just on these new TLDs - and they are ASCII!