RFC 5321 limits email addresses to 7 bit US-ASCII encoding. RFC 6531 (a fairly new spec) allows email addresses in SMTP commands and IMF headers to be encoded in UTF-8. This SMTP extension makes internationalized email addresses (e.g., pelé@example.com) possible.
An SMTP server advertises support for internationalized email by replying to the
EHLO command with the
250-smtp.example.com at your service 250 SMTPUTF8
An SMTP client utilizes this extension with the
MAIL FROM:<pelé@example.com> SMTPUTF8
Question: Are there any SMTP servers or email clients that support SMTPUTF8?