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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 SMTPUTF8 keyword:

250-smtp.example.com at your service
250 SMTPUTF8

An SMTP client utilizes this extension with the MAIL command:

MAIL FROM:<pelé@example.com> SMTPUTF8 

Question: Are there any SMTP servers or email clients that support SMTPUTF8?

closed as off-topic by Jenny D, Michael Hampton Sep 3 '14 at 16:01

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  • Not according to WikiPedia. – Ladadadada Jan 17 '13 at 13:16
  • I've read that, thanks, but WP is not always current. :-( – james.garriss Jan 17 '13 at 13:26
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    The hold is not appropriate. Read the question. It's not a request for a recommendation. It's asking for the state of the art. – james.garriss Sep 3 '14 at 19:43
  • LOL. Earned a silver badge for a Notable Question, yet it was closed as off-topic. – james.garriss Jul 5 '17 at 11:08
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Postfix supports a subset of SMTPUTF8 since version 2.12: http://www.postfix.org/SMTPUTF8_README.html

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Edit: This answer is no longer true.

As far as I can tell, at this time (Feb 2013) there are no SMTP servers or email clients that support SMTPUTF8.

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