Could not send email from android app

Question

I'm trying to send email from an android application I'm developing and I've found a source code in order to do it. But I get this errors:

06-18 17:17:50.593 14791-14791/com.mh2.ilmartino E/MailApp﹕ Could not send email android.os.NetworkOnMainThreadException at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1145) at java.net.InetAddress.lookupHostByName(InetAddress.java:385) at java.net.InetAddress.getLocalHost(InetAddress.java:365) at javax.mail.internet.InternetAddress.getLocalAddress(InternetAddress.java:517) at javax.mail.internet.UniqueValue.getUniqueMessageIDValue(UniqueValue.java:99) at javax.mail.internet.MimeMessage.updateMessageID(MimeMessage.java:2054) at javax.mail.internet.MimeMessage.updateHeaders(MimeMessage.java:2076) at javax.mail.internet.MimeMessage.saveChanges(MimeMessage.java:2042) at javax.mail.Transport.send(Transport.java:117) at com.mh2.ilmartino.Mail.send(Mail.java:104) at com.mh2.ilmartino.Segnala$1.onClick(Segnala.java:88) at android.view.View.performClick(View.java:4438) at android.view.View$PerformClick.run(View.java:18422) at android.os.Handler.handleCallback(Handler.java:733) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:136) at android.app.ActivityThread.main(ActivityThread.java:5001) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:515) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601) at dalvik.system.NativeStart.main(Native Method)

Here's my code. (I've obfuscated email address and password on purpose) Mail.java:

package com.mh2.ilmartino;

import java.util.Date;
import java.util.Properties;
import javax.activation.CommandMap;
import javax.activation.DataHandler;
import javax.activation.DataSource;
import javax.activation.FileDataSource;
import javax.activation.MailcapCommandMap;
import javax.mail.BodyPart;
import javax.mail.Multipart;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeBodyPart;
import javax.mail.internet.MimeMessage;
import javax.mail.internet.MimeMultipart;


public class Mail extends javax.mail.Authenticator {
    private String _user;
    private String _pass;

    private String[] _to;
    private String _from;

    private String _port;
    private String _sport;

    private String _host;

    private String _subject;
    private String _body;

    private boolean _auth;

    private boolean _debuggable;

    private Multipart _multipart;


    public Mail() {
        _host = "smtp.gmail.com"; // default smtp server
        _port = "465"; // default smtp port
        _sport = "465"; // default socketfactory port

        _user = "USER"; // username
        _pass = "MYPASS"; // password
        _from = "lamadonna"; // email sent from
        _subject = "segnalazione"; // email subject
        _body = "coddio"; // email body

        _debuggable = false; // debug mode on or off - default off
        _auth = true; // smtp authentication - default on

        _multipart = new MimeMultipart();

        // There is something wrong with MailCap, javamail can not find a handler for the multipart/mixed part, so this bit needs to be added.
        MailcapCommandMap mc = (MailcapCommandMap) CommandMap.getDefaultCommandMap();
        mc.addMailcap("text/html;; x-java-content-handler=com.sun.mail.handlers.text_html");
        mc.addMailcap("text/xml;; x-java-content-handler=com.sun.mail.handlers.text_xml");
        mc.addMailcap("text/plain;; x-java-content-handler=com.sun.mail.handlers.text_plain");
        mc.addMailcap("multipart/*;; x-java-content-handler=com.sun.mail.handlers.multipart_mixed");
        mc.addMailcap("message/rfc822;; x-java-content-handler=com.sun.mail.handlers.message_rfc822");
        CommandMap.setDefaultCommandMap(mc);
    }

    public Mail(String user, String pass) {
        this();

        _user = user;
        _pass = pass;
    }

    public boolean send() throws Exception {
        Properties props = _setProperties();

        if(!_user.equals("") && !_pass.equals("") && _to.length > 0 && !_from.equals("") && !_subject.equals("") && !_body.equals("")) {
            Session session = Session.getInstance(props, this);

            MimeMessage msg = new MimeMessage(session);

            msg.setFrom(new InternetAddress(_from));

            InternetAddress[] addressTo = new InternetAddress[_to.length];
            for (int i = 0; i < _to.length; i++) {
                addressTo[i] = new InternetAddress(_to[i]);
            }
            msg.setRecipients(MimeMessage.RecipientType.TO, addressTo);

            msg.setSubject(_subject);
            msg.setSentDate(new Date());

            // setup message body
            BodyPart messageBodyPart = new MimeBodyPart();
            messageBodyPart.setText(_body);
            _multipart.addBodyPart(messageBodyPart);

            // Put parts in message
            msg.setContent(_multipart);

            // send email
            Transport.send(msg);

            return true;
        } else {
            return false;
        }
    }

    public void addAttachment(String filename) throws Exception {
        BodyPart messageBodyPart = new MimeBodyPart();
        DataSource source = new FileDataSource(filename);
        messageBodyPart.setDataHandler(new DataHandler(source));
        messageBodyPart.setFileName(filename);

        _multipart.addBodyPart(messageBodyPart);
    }

    @Override
    public PasswordAuthentication getPasswordAuthentication() {
        return new PasswordAuthentication(_user, _pass);
    }

    private Properties _setProperties() {
        Properties props = new Properties();

        props.put("mail.smtp.host", _host);

        if(_debuggable) {
            props.put("mail.debug", "true");
        }

        if(_auth) {
            props.put("mail.smtp.auth", "true");
        }

        props.put("mail.smtp.port", _port);
        props.put("mail.smtp.socketFactory.port", _sport);
        props.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
        props.put("mail.smtp.socketFactory.fallback", "false");

        return props;
    }

    // the getters and setters
    public String getBody() {
        return _body;
    }

    public void setBody(String _body) {
        this._body = _body;
    }

    public void setFrom(String _from) {
        this._from = _from;
    }
    public void setSubject(String _subject) {
        this._subject = _subject;
    }
    public void setTo(String[] _to) {
        this._to = _to;
    }
}

And Segnala.java:

package com.mh2.ilmartino;

import android.app.Activity;
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.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import java.util.Date;
import java.util.Properties;
import javax.activation.CommandMap;
import javax.activation.DataHandler;
import javax.activation.DataSource;
import javax.activation.FileDataSource;
import javax.activation.MailcapCommandMap;
import javax.mail.BodyPart;
import javax.mail.Multipart;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeBodyPart;
import javax.mail.internet.MimeMessage;
import javax.mail.internet.MimeMultipart;



public class Segnala extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_segnala);

        Button inviaS = (Button) findViewById(R.id.button);
        inviaS.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View arg0) {
                final EditText campoDescrizione = (EditText) findViewById(R.id.editText);
                String descrizione = campoDescrizione.getText().toString();

                final EditText campoLuogo = (EditText) findViewById(R.id.editText2);
                String luogo = campoLuogo.getText().toString();


                /*
                Intent emailIntent = new Intent(Intent.ACTION_SENDTO);
                emailIntent.setData(Uri.parse("mailto:" + "[email protected]"));
                emailIntent.putExtra(Intent.EXTRA_SUBJECT, "My email's subject");
                emailIntent.putExtra(Intent.EXTRA_TEXT, "My email's body");

                try {
                    startActivity(Intent.createChooser(emailIntent, "Send email using..."));
                } catch (android.content.ActivityNotFoundException ex) {
                    Toast.makeText(Segnala.this, "No email clients installed.", Toast.LENGTH_SHORT).show();

                }*/
                /*
                Intent sendIntent;

                sendIntent = new Intent(Intent.ACTION_SEND);
                sendIntent.putExtra(Intent.EXTRA_SUBJECT, "Test Subject");
                sendIntent.putExtra(Intent.EXTRA_TEXT, "Test Text");
                sendIntent.putExtra(Intent.EXTRA_STREAM, Uri.parse("file://" /*+ fileName));
                sendIntent.setData(Uri.parse("mailto:" + "[email protected]"));
                sendIntent.setType("image/jpeg");

                startActivity(Intent.createChooser(sendIntent, "Send Mail"));*/
                Mail m = new Mail(*MYEMAILADDRESS*, *MYPASSWORD*);

                String[] toArr = {"[email protected]"};

                m.setTo(toArr);
                m.setFrom("[email protected]");
                m.setSubject("This is an email sent using my Mail JavaMail wrapper from an Android device.");
                m.setBody(luogo + " " + descrizione);

                try {
                   // m.addAttachment("/sdcard/filelocation");

                    if(m.send()) {
                        Toast.makeText(Segnala.this, "Email was sent successfully.", Toast.LENGTH_LONG).show();
                    } else {
                        Toast.makeText(Segnala.this, "Email was not sent.", Toast.LENGTH_LONG).show();
                    }
                } catch(Exception e) {
                    //Toast.makeText(MailApp.this, "There was a problem sending the email.", Toast.LENGTH_LONG).show();
                    Log.e("MailApp", "Could not send email", e);
                }
            }

        });

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_segnala, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }



}

I cannot understan where is the error... Could you please help me? Thanks in advance.