code: public static void sendMessage(final Context context, final String subject, final String body, final String toAddress) {
          final Intent intent;
          if (toAddress != null && !"".equals(toAddress)) {
              intent = new Intent(Intent.ACTION_SENDTO, Uri.fromParts("mailto", toAddress, null));
          } else {
              intent = new Intent(Intent.ACTION_SEND);
          }
          intent.setType("text/plain");
          if (subject != null && !"".equals(subject)) {
              intent.putExtra(Intent.EXTRA_SUBJECT, subject);
          }
          if (body != null && !"".equals(body)) {
              intent.putExtra(Intent.EXTRA_TEXT, body);
          }
          context.startActivity(Intent.createChooser(intent, "Send message..."));
      }
docs: Starts a {@code ACTION_SENDTO} system {@code Intent} used to create a message (email, sms, text, etc).
  @param subject   Optional subject line.
  @param body      Optional message body.
  @param toAddress Optional "to" address.