Sending mail to recipients with Japanese names

[appleseed]

Hi all,
when sending mail, it works fine unless I send to an address with a Display Name containing Japanese chars.
For example,
Recipient: 以

will fail. there aren't any errors in the errors/sendmail/apache logs, even with log_level set to 8.
the mail goes right into the exim queue, and can't be delivered.

the exim logs receive this:
 <= <> R=1HjEla-00014m-D3 U=mail P=local S=2131
so no recipient or sender.
rather than something like:
 <= [email protected] U=www P=local S=600 id=nnnnnnnnnnnnnnnnnnnnnnnnnn
 => [email protected] R=dnslookup T=remote_smtp H=gmail-smtp-in

this server is running the latest exim, openldap and roundcube.

any ideas?