Sending Email in Android using JavaMail API without using the default/built-in app

To send an email in Android using the JavaMail API without using the default/built-in app, you can use the following steps:

Download the JavaMail API from the following link: https://eclipse-ee4j.github.io/mail/
Add the INTERNET permission to your AndroidManifest.xml file:

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

Add the JavaMail Android dependencies to your app-level build.gradle file:

implementation 'com.sun.mail:android-mail:1.6.7'
implementation 'com.sun.mail:android-activation:1.6.7'

Create a new Java class to send the email and import the necessary classes from the JavaMail API:

import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
import javax.mail.Authenticator;
import javax.mail.PasswordAuthentication;
import java.util.Properties;
import java.util.concurrent.Executors;

Use the following code to create a session and send the email:

// Set the email properties
Properties props = new Properties();
props.put("mail.smtp.auth", "true");
props.put("mail.smtp.starttls.enable", "true");
props.put("mail.smtp.host", "smtp.gmail.com");
props.put("mail.smtp.port", "587");

// Create a session with the email properties
Session session = Session.getInstance(props, new Authenticator() {
    protected PasswordAuthentication getPasswordAuthentication() {
        return new PasswordAuthentication("[email protected]", "your_password");
    }
});

try {
    // Create the email message
    Message message = new MimeMessage(session);
    message.setFrom(new InternetAddress("[email protected]"));
    message.setRecipients(Message.RecipientType.TO, InternetAddress.parse("[email protected]"));
    message.setSubject("Email Subject");
    message.setText("Email body");

    // Send the email on a background thread to prevent NetworkOnMainThreadException
    Executors.newSingleThreadExecutor().execute(() -> {
        try {
            Transport.send(message);
            System.out.println("Email sent successfully!");
        } catch (MessagingException e) {
            e.printStackTrace();
        }
    });
} catch (MessagingException e) {
    e.printStackTrace();
}

Important Android Development Notes:

javax.* INTERNET javax.* packages were removed from the platform, so you must use the Android-specific JavaMail port (added in step 3) to compile on modern SDK versions.
Network operations must run on a background thread to avoid NetworkOnMainThreadException.
The API does not provide built-in delivery confirmation; verify successful sending by checking the recipient's inbox or the sender's "Sent" folder.
Gmail requires an App-Specific Password for SMTP authentication. Standard account passwords will be rejected by Google's security policies. Generate one in your Google Account settings under Security > App Passwords.