I just registered account "testbug" with email address "testbug@gñail.com" here so the devs can see the error logged. You can safely remove that account.
Zend_Mail_Protocol_Exception: Email to testbug@gñail.com failed: 5.1.3 Bad recipient address syntax - library/Zend/Mail/Protocol/Abstract.php:431
As far as I understand, that is a valid domain when it comes to IDNs, but that's not something we really have explicit support for (though you can always enter the punycode version), so I've basically disabled IDN support in emails.
