How to save MailMessage into eml file by Reflection on .net framework 4.5?

/// 

        /// HACK - SmtpClient does not give access to filenames when outputting e-mails to disk.  The following extension method
        /// uses reflection to call the internal MailWriter type so that mails can be created with a specified filename.
        /// 
        /// Code taken from: http://www.codeproject.com/KB/IP/smtpclientext.aspx
        /// 
        /// Mail message to be serialized./// Filename of mail message.public static void Save(this MailMessage Message, string FileName)
        {
            // TODO: See if the Mono framework has serialization code we can use.

            Assembly assembly = typeof(SmtpClient).Assembly;
            Type _mailWriterType =
              assembly.GetType("System.Net.Mail.MailWriter");

            using (FileStream _fileStream =
                   new FileStream(FileName, FileMode.Create))
            {
                // Get reflection info for MailWriter contructor
                ConstructorInfo _mailWriterContructor =
                    _mailWriterType.GetConstructor(
                        BindingFlags.Instance | BindingFlags.NonPublic,
                        null,
                        new Type[] { typeof(Stream) },
                        null);

                // Construct MailWriter object with our FileStream
                object _mailWriter =
                  _mailWriterContructor.Invoke(new object[] { _fileStream });

                // Get reflection info for Send() method on MailMessage
                MethodInfo _sendMethod =
                    typeof(MailMessage).GetMethod(
                        "Send",
                        BindingFlags.Instance | BindingFlags.NonPublic);

                // Call method passing in MailWriter
                _sendMethod.Invoke(
                    Message,
                    BindingFlags.Instance | BindingFlags.NonPublic,
                    null,
                    new object[] { _mailWriter, true, true },
                    null);

                // Finally get reflection info for Close() method on our MailWriter
                MethodInfo _closeMethod =
                    _mailWriter.GetType().GetMethod(
                        "Close",
                        BindingFlags.Instance | BindingFlags.NonPublic);

                // Call close method
                _closeMethod.Invoke(
                    _mailWriter,
                    BindingFlags.Instance | BindingFlags.NonPublic,
                    null,
                    new object[] { },
                    null);
            }
        }