4.1 FH_HOST_ALMOST_IP The host almost looks like an IP addr.
We’ve also been experiencing this - normally when we (or our clients) send using our ISP SMTP server rather than the JohoHost one. I just haven’t had time yet to log a ticket.
That’s probably causing the bounce. By using correct MIME/charset, your mails should go fine irrespective of the language. Base-64 encoding increases resource requirements on anti-spam gateways and allows to send arbitrary data.