Convert string to Stream

   private void AddAttachmentFromStream(MailMessage message, String data, String attachmentName)
  {
    MemoryStream stream = new MemoryStream(UTF32Encoding.Default.GetBytes(data));
    stream.Position = 0;
  // Create a new attachment, add the attachment to the supplied message.
    Attachment att = new Attachment(stream, attachmentName);
    message.Attachments.Add(att);
  }