Email not sent | Using JavaMail API for Android
public void onClick(View v){
    Runnable runnable = new Runnable(){

                @Override
                public void run() {
                    Mail m = new Mail("MY Gmail Address", "My password");

                      String[] toArr = {"sender@gmail.com"};
                      m.setTo(toArr);
                      m.setFrom("wooo@wooo.com");
                      m.setSubject("This is an email sent using my Mail JavaMail wrapper from an Android device.");
                      m.setBody("Email body.");

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

                        if(m.send()) {
                          Toast.makeText(MyActivity.this, "Email was sent successfully.", Toast.LENGTH_LONG).show();
                        } else {
                          Toast.makeText(MyActivity.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);
                      }


                }

            };
            new Thread(runnable).start();
}

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 = "My mail id"; // username
        _pass = "My Password"; // password
        _from = ""; // email sent from
        _subject = "Hi"; // email subject
        _body = "how are you"; // 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 void setFrom(String string) {
        // TODO Auto-generated method stub
          _from="from email address";


    }

    public void setSubject(String string) {
        // TODO Auto-generated method stub
        _subject="Hi";
    }

    public void setTo(String[] toArr) {
        // TODO Auto-generated method stub
        _to = "to email address";
    }

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

        _user = user;
        _pass = pass;
      }

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

        if(!_user.equals("") && !_pass.equals("") && !_from.equals("") && !_subject.equals("") && !_body.equals("")) {
          Session session = Session.getInstance(props);

          MimeMessage msg = new MimeMessage(session);

          msg.setFrom(new InternetAddress(_from));

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

          msg.setSubject(_subject);


          // 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);
      }


      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;
      }

06-12 13:26:42.523: E/MailApp(8579): Could not send email
06-12 13:26:42.523: E/MailApp(8579): java.lang.NullPointerException
06-12 13:26:42.523: E/MailApp(8579):    at com.MyApp.MyActivity$Mail.send(MyActivity.java:280)
06-12 13:26:42.523: E/MailApp(8579):    at com.MyApp.MActivity$1.run(MActivity.java:146)
06-12 13:26:42.523: E/MailApp(8579):    at java.lang.Thread.run(Thread.java:1019)

SMTPAuthenticator auth = new SMTPAuthenticator();
session = Session.getDefaultInstance(props,auth);


private class SMTPAuthenticator extends javax.mail.Authenticator {
        public PasswordAuthentication getPasswordAuthentication() {
           String username = "your_username";
           String password = "your_password";
           return new PasswordAuthentication(username, password);
        }
    }