Hey Rudolf,
Thanks for the question. Currently, we do not support SMTPUTF8 as that would also require supporting internationalized email addresses. We do have a task to get this feature added to SmarterMail in our backlog but I do not have a timeframe for when this will be supported.
I hope this answers your question.
Kind Regards,
Zach Sylvester
Software Developer
SmarterTools Inc.
www.smartertools.com