You'll need to look at the actual HTML content of the e-mails that it is sending – does the header specify UTF-8 encoding? There should be some kind of template somewhere into which the body of the message will be inserted for rendering, and that template should specify a complete HTML package including the "head" tag where the encoding spec should be. Next, you must also verify that your e-mail client understands this tag and can, in fact, render UTF-8 characters. Some of them are smart; some of them are stupid.