Google This document describes some scenarios in which one can imagine internationalized email addresses deployed, and tries to draw some conclusions about what's acceptable and what's not for users in those scenarios. One possible set of extensions that can work in these scenarios is those described in the UTF8SMTP extension documents.Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].