Internationalization
The IETF conducts a technical and standards working group devoted to internationalization issues of email addresses, entitled Email Address Internationalization (EAI, also known as IMA – Internationalized Mail Address). This group produced RFCs 6530, 6531, 6532, and 6533, and continues to work on additional EAI related RFCs.
The IETF's EAI Working group published RFC 6530 "Overview and Framework for Internationalized Email", which enabled non-ASCII characters to be used in both the local and domain parts of an email address. RFC 6530 provides for email based on the UTF-8 encoding, which permits the full repertoire of Unicode. RFC 6531 provides a mechanism for SMTP servers to negotiate transmission of the SMTPUTF8 content.
The basic EAI concepts involve exchanging mail in UTF-8. Though the original proposal included a downgrading mechanisms for legacy systems this has now been dropped. The local servers are responsible for the "local" part of the address, whereas the domain portion would be restricted by the rules of internationalized domain names, though still transmitted in UTF-8. The mail server is also responsible for any mapping mechanism between the IMA form and any ASCII alias.
EAI enables users to have a localized address in a native language script or character set, as well as an ASCII form for communicating with legacy systems or for script-independent use. Applications that recognize internationalized domain names and mail addresses must have facilities to convert these representations.
Significant demand for such addresses is expected in China, Japan, Russia, and other markets that have large user bases in a non-Latin based writing system.
Read more about this topic: Email Address