encoding to UTF-8 in email

I have a client that is receiving email incorrectly encoded. I am using the System.Net.Mail class and setting the body encoding to UTF-8. I have done a bit of reading and since I have to set the body of the email as a string encoding the data to a UTF-8 byte array really does nothing for me since I have to convert is back to a string that is UTF-16. Correct?

when I send:Il s'agit d'un message de test pour déterminer comment le système va gérer les messages envoyés à l'aide des caractères français. Merci et bonne journée.

They see: *Il s'agit d'un message de test pour déterminer comment le système va gérer les messages envoyés à l'aide des caractères français.

Merci et bonne journée.*

I have tried different encodings on the email, but I am really suspecting that the client is incorrectly decoding the email since my email client displays this correctly. Am I missing something? Is there something else that can be done?

code below

SmtpMailService.SendMail(string.Empty, toAddress, "emailaddress@emai.com", "", subject, sb.ToString(), false);

 public static bool SendMail(string fromAddress, string toAddress, string ccAddress, string bccAddress, string subject, string body, bool isHtmlBody)
    {

        if (String.IsNullOrEmpty(toAddress)) return false;
        var toMailAddress = new MailAddress(toAddress);

        var fromMailAddress = new MailAddress(String.IsNullOrEmpty(fromAddress) ? DefaultFromAddress : fromAddress);

        var mailMessage = new MailMessage(fromMailAddress, toMailAddress);

        if (!String.IsNullOrEmpty(ccAddress))
        {
            mailMessage.CC.Add(new MailAddress(ccAddress));
        }

        if (!String.IsNullOrEmpty(bccAddress))
        {
            mailMessage.Bcc.Add(new MailAddress(bccAddress));
        }

        if (!string.IsNullOrEmpty(fromAddress)) mailMessage.Headers.Add("Reply-To", fromAddress);

        mailMessage.Subject = subject;
        mailMessage.IsBodyHtml = isHtmlBody;
        mailMessage.Body = body;
        mailMessage.BodyEncoding = System.Text.Encoding.UTF8;

        var enableSslCfg = ConfigurationManager.AppSettings["Email.Ssl"];
        var enableSsl = string.IsNullOrEmpty(enableSslCfg) || bool.Parse(enableSslCfg);
        var client = new SmtpClient {EnableSsl = enableSsl};

        client.Send(mailMessage);


        return true;
    }