Similar experience with IDN domains. Most places altogether reject them, but those which accept them, only a subset accept IDN recipient in the mail address.
Personally I did not enable SMTPUTF8 support in my Postfix due to the lack of Dovecot support.
[1] https://tools.ietf.org/html/rfc6531 [2] http://www.postfix.org/SMTPUTF8_README.html