Sendmail Java - Android Studio

Good morning, I'm developing an application, where I have the following doubt. I want to send an e-mail form using Intent's. The code is apparently OK, but when I click the "Send" button the program does nothing. Please, I would like you to help me. Here is the Java and XML code:

JAVA

package pt.penafielverde.serpeagu.serpaguv110.agu;
import android.content.Intent;
import android.net.Uri;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class enviarmail extends AppCompatActivity {
    Button enviar = findViewById(R.id.enviar);
    final EditText assunto = findViewById(R.id.assunto);
    EditText operador = findViewById(R.id.operador);
    final EditText corpoemail = findViewById(R.id.corpoemail);
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_enviar_email);
        enviar.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                sendMail();
                assunto.setText("");
                operador.setText("");
                corpoemail.setText("");
            }
            private void sendMail() {
                String recipientList = "[email protected]";
                String[] recipients = recipientList.split(",");
                String subject = assunto.getText().toString();
                String message = corpoemail.getText().toString();
                Intent intent = new Intent(Intent.ACTION_SEND);
                intent.putExtra(Intent.EXTRA_EMAIL, recipients);
                intent.putExtra(Intent.EXTRA_SUBJECT, subject);
                intent.putExtra(Intent.EXTRA_TEXT, message + "Mensagem enviada por," + operador);
                intent.setType("message/rfc822");
                startActivity(Intent.createChooser(intent, "Escolha o cliente email, por onde deseja enviar a mensagem :"));
            }
            ;
        });
    }
}

XML

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="pt.penafielverde.serpeagu.serpaguv110.agu.enviarmail">

    <TextView
        android:id="@+id/textView10"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        android:layout_marginStart="66dp"
        android:layout_marginTop="51dp"
        android:text="Operador.:" />

    <TextView
        android:id="@+id/textView11"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="14dp"
        android:text="COMUNICAÇÃO "
        android:textColor="@android:color/holo_green_light"
        android:textStyle="bold" />

    <TextView
        android:id="@+id/assunto_textview"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignEnd="@+id/textView10"
        android:layout_alignParentTop="true"
        android:layout_marginTop="81dp"
        android:text="Assunto.:" />

    <EditText
        android:id="@+id/operador"
        android:layout_width="wrap_content"
        android:layout_height="36dp"
        android:layout_alignBaseline="@+id/textView10"
        android:layout_toEndOf="@+id/textView10"
        android:ems="10"
        android:inputType="textPersonName"
        android:textSize="12sp" />

    <EditText
        android:id="@+id/assunto"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/textView10"
        android:layout_toEndOf="@+id/textView10"
        android:ems="10"
        android:inputType="textPersonName"
        android:textSize="12sp" />

    <EditText
        android:id="@+id/corpoemail"
        android:layout_width="334dp"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="154dp"
        android:ems="10"
        android:inputType="textMultiLine" />

    <TextView
        android:id="@+id/textView13"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_above="@+id/corpoemail"
        android:layout_alignStart="@+id/corpoemail"
        android:layout_marginBottom="-154dp"
        android:text="Descrição da Anómalia" />

    <Button
        android:id="@+id/enviar"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="17dp"
        android:text="enviar" />
</RelativeLayout>