What is address internationalization (EAI)?

Address internationalization, often shortened to EAI, allows email addresses to use non Latin characters in both the local part and the domain. This means an address can contain characters from Greek, Cyrillic, Japanese, and many other scripts rather than only basic ASCII.

Behind the scenes, EAI relies on the SMTPUTF8 extension described in RFC six five three one. Domains are handled through IDNA and punycode so that the human readable version can include native characters while the underlying DNS system still works reliably.

Support is not universal. Many older systems and some web forms still assume plain ASCII only. Because of this, many senders keep a traditional ASCII address as their primary reply address even when they experiment with EAI addresses.