在Microsoft.Exchange.WebServices.Data.emailmessage.culture中发送

我试图通过交换服务发送XML字符串，这是我的代码

ServicePointManager.Expect100Continue = true;
            ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3;
            ServicePointManager.ServerCertificateValidationCallback = delegate(object s, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors) { return true; };

            exService.UseDefaultCredentials = false;
            exService.Credentials = new NetworkCredential("set of credentials");
            exService.Url = new Uri("https://url");
 public void SendMail(string subject, string body, string to)
        {
            lock (this)
            {
            EmailMessage msg = new EmailMessage(exService);
#if DEBUG
            msg.ToRecipients.Add("test@address.com");
#else
            msg.ToRecipients.Add(to);
#endif
            msg.Body = body;
            msg.Subject = subject;
            msg.Send();
}}

subject和to就像你猜测这些信息的字符串对象一样。主体是由XML组成的字符串。我以前用HTML和电子邮件使用过这个代码，结果很好。我需要将它与XML一起用于桌面或服务应用程序。目前，当我输入XML字符串时，电子邮件显示为空白，但如果我输入字符串文字，它会显示良好。当邮件到达Outlook时，Outlook会以HTML而不是纯文本的形式报告邮件。我需要添加什么才能使XML在收到的电子邮件中正常显示?