International characters in email-addresses / diacritics

[lawik]

I've received failed validation on a number of addresses containing the swedish characters åäö as well as the slightly more french é. From what I've gathered any UTF-8 is valid (https://en.wikipedia.org/wiki/International_email#Email_addresses). It might not be nice and I will consider rejecting these anyway, but what kind of ruleset does Flanker actually run on?