RE: "International" email addresses

> IDN rules are different for each zone. They are currently described in ways that make it difficult to validate them mechanically.

Local parts are different for each zone too, most of the legal SMTP address styles won’t ever be assigned on most servers.

Clearly resolving the domain is an indicator of whether or not it’s “real”, however you can still have the high-level validation that checks for overall conformance.  Some zones may be more strict, but none will be more lax.  (Similar to local parts).

-Shawn