How do I know if the email was actually sent?

I am using a code for sending e-mail, I call the e-mail service and choose a certain e-mail that is already configured on the mobile phone. It's all working normally, however I want to put an alert after sending this email but I can not display it at the right time because I do not have a positive or negative response from sending that email. How do I know that the email was actually sent? Here's my code ...

                Intent sendEmail = new Intent(Intent.ACTION_SEND);
                sendEmail.putExtra(Intent.EXTRA_EMAIL, new String[]{to});
                sendEmail.putExtra(Intent.EXTRA_SUBJECT, assunto);
                sendEmail.putExtra(Intent.EXTRA_CC, new String[]{email});
                sendEmail.putExtra(Intent.EXTRA_STREAM, imageUri);
                sendEmail.putExtra(Intent.EXTRA_TEXT, "texto...");

                sendEmail.setType("message/rfc822");

                startActivity(Intent.createChooser
                     (sendEmail, "Enviar o e-mail com: "));

                AlertDialog.Builder alert = new AlertDialog.Builder(activity);
                alert.setTitle("Obrigado pelo contato !");
                alert.setMessage("texto...");
                alert.setPositiveButton("OK", null);
                alert.show();