sending mail from android application..(need to add INTERNET permission in manifest and need to add jar library files, use this link to download (https://drive.google.com/file/d/1L488o5wIDQE-X9ajq2EDpp7asjmjd3fp/view?usp=sharing))

MailService.java

package com.example.salasuresh.androidpractice.sendmail;

import android.os.AsyncTask;

import java.io.UnsupportedEncodingException;
import java.util.Properties;

import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.AddressException;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;

public class MailService {
    private static final String USER_NAME = "<SENDER EMAIL ID>";
    private static final String PASSWORD = "<SENDER EMAIL PASSWORD>";
    private static final String PERSONAL = "Send Mail Demo";

    public void sendMail(String email, String subject, String messageBody) {
        try {
            Message message = createMessage(email, subject, messageBody, createSession());
            new SendMailTask().execute(message);
        } catch (AddressException e) {
            e.printStackTrace();
        } catch (MessagingException e) {
            e.printStackTrace();
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
    }

    private Message createMessage(String email, String subject, String messageBody, Session session) throws MessagingException, UnsupportedEncodingException {
        Message message = new MimeMessage(session);
        message.setFrom(new InternetAddress(USER_NAME, PERSONAL));
        message.addRecipient(Message.RecipientType.TO, new InternetAddress(email, email));
        message.setSubject(subject);
        message.setText(messageBody);
        return message;
    }

    private Session createSession() {
        Properties properties = new Properties();
        properties.put("mail.smtp.auth", "true");
        properties.put("mail.smtp.starttls.enable", "true");
        properties.put("mail.smtp.host", "smtp.gmail.com");
        properties.put("mail.smtp.port", "587");

        return Session.getInstance(properties, new javax.mail.Authenticator() {
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(USER_NAME, PASSWORD);
            }
        });
    }

    private class SendMailTask extends AsyncTask<Message, Void, Void> {
        @Override
        protected Void doInBackground(Message... messages) {
            try {
                Transport.send(messages[0]);
            } catch (MessagingException e) {
                e.printStackTrace();
            }
            return null;
        }
    }
}

SendMailActivity.java

package com.example.salasuresh.androidpractice.sendmail;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;

import com.example.salasuresh.androidpractice.R;

public class SendMailActivity extends AppCompatActivity {

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

        Button sendButton = findViewById(R.id.button_common);
        sendButton.setVisibility(View.VISIBLE);
        sendButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String email = "<RECEIVER EMAIL ID>";
                String subject = "TEST SUBJECT FROM PROGRAM";
                String message = "TEST MESSAGE FROM PROGRAM";
                new MailService().sendMail(email, subject, message);
            }
        });
    }

}