[Android] How to send email(Gmail) programmatically without launching a third party app (new intent)

First you need following "javamail-android" libraries: (download)

• additionnal.jar 
• mail.jar
• activation.jar

Copy them to \libs folder and add copied jars to your project library.

You need following permissions:

   <uses-permission android:name="android.permission.GET_ACCOUNTS" />  
   <uses-permission android:name="android.permission.INTERNET" />  
   <uses-permission android:name="android.permission.USE_CREDENTIALS" />  

OAuth2Authenticator.java:

   
 import android.accounts.Account;  
 import android.accounts.AccountManager;  
 import android.accounts.AccountManagerCallback;  
 import android.accounts.AccountManagerFuture;  
 import android.app.Activity;  
 import android.os.AsyncTask;  
 import android.os.Bundle;  
 import android.util.Log;  
   
 import com.sun.mail.smtp.SMTPTransport;  
 import com.sun.mail.util.BASE64EncoderStream;  
   
 import java.util.Properties;  
   
 import javax.activation.DataHandler;  
 import javax.mail.Message;  
 import javax.mail.Session;  
 import javax.mail.URLName;  
 import javax.mail.internet.InternetAddress;  
 import javax.mail.internet.MimeMessage;  
 import javax.mail.util.ByteArrayDataSource;  
   
   
 public class OAuth2Authenticator {  
   
   private static Session mSession;  
   
   private AccountManager mAccountManager;  
   private String mToken;  
   private Account mAccount = null;  
   private Activity mActivity;  
   private static String TEST_ACCOUNT_EMAIL = "(your_account_that_is_added_to_Android_device)@gmail.com";  
   
   public OAuth2Authenticator(Activity activity) {  
     mActivity = activity;  
     mAccountManager = AccountManager.get(mActivity);  
   
     Account[] accounts = mAccountManager.getAccounts();  
   
     // For this tutorial, we manually set the email account(TEST_ACCOUNT_EMAIL). However, you should create some kind of UI for users to select the Gmail account  
     for (Account a : accounts) {  
       if (a.name.equals(TEST_ACCOUNT_EMAIL) && a.type.equals("com.google")) {  
         mAccount = a;  
       }  
     }  
     if (mAccount != null) {  
       AccountManagerFuture<Bundle> future = mAccountManager.getAuthToken(mAccount, "oauth2:https://mail.google.com/", null, mActivity, new OnTokenAcquired(), null);  
     }  
   
   }  
   
   private class OnTokenAcquired implements AccountManagerCallback<Bundle> {  
     @Override  
     public void run(AccountManagerFuture<Bundle> result) {  
       try {  
         Bundle bundle = result.getResult();  
         mToken = bundle.getString(AccountManager.KEY_AUTHTOKEN);  
         new SendMailTask().execute();  
       } catch (Exception e) {  
         Log.e("OnTokenAcquired", e.getMessage());  
       }  
     }  
   }  
   
   private class SendMailTask extends AsyncTask<Void, Void, Void> {  
   
     @Override  
     protected Void doInBackground(Void... params) {  
       try {  
         sendMail("subject", "body message", TEST_ACCOUNT_EMAIL, mToken, "(recipient_address)@(somemail).com");  
       } catch (Exception e) {  
         Log.e("SendMailTask", "error:" + e.getMessage());  
       }  
       return null;  
     }  
   }  
   
   private SMTPTransport connectToSmtp(String host, int port, String userEmail,  
                     String oauthToken, boolean debug) throws Exception {  
   
     Properties props = new Properties();  
     props.put("mail.smtp.starttls.enable", "true");  
     props.put("mail.smtp.starttls.required", "true");  
     props.put("mail.smtp.sasl.enable", "false");  
     mSession = Session.getInstance(props);  
     mSession.setDebug(debug);  
     final URLName unusedUrlName = null;  
     SMTPTransport transport = new SMTPTransport(mSession, unusedUrlName);  
     // If the password is non-null, SMTP tries to do AUTH LOGIN.  
     final String emptyPassword = null;  
     transport.connect(host, port, userEmail, emptyPassword);  
     byte[] response = String.format("user=%s\1auth=Bearer %s\1\1", userEmail, oauthToken).getBytes();  
     response = BASE64EncoderStream.encode(response);  
     transport.issueCommand("AUTH XOAUTH2 " + new String(response), 235);  
     return transport;  
   }  
   
   public synchronized void sendMail(String subject, String body, String user,  
                    String oauthToken, String recipients) {  
     try {  
   
       SMTPTransport smtpTransport = connectToSmtp("smtp.gmail.com",  
           587,  
           user,  
           oauthToken,  
           true);  
       MimeMessage message = new MimeMessage(mSession);  
       DataHandler handler = new DataHandler(new ByteArrayDataSource(body.getBytes(), "text/plain"));  
       message.setSender(new InternetAddress(user));  
       message.setSubject(subject);  
       message.setDataHandler(handler);  
       if (recipients.indexOf(',') > 0)  
         message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(recipients));  
       else  
         message.setRecipient(Message.RecipientType.TO, new InternetAddress(recipients));  
       smtpTransport.sendMessage(message, message.getAllRecipients());  
     } catch (Exception e) {  
       Log.e("sendMail", e.getMessage());  
     }  
   }  
 }  

MainActivity.java:

 new OAuth2Authenticator(this);