Solution: Background Email Sender

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class EmailSender {
    public static void main(String[] args) {
        String[] emails = {
            "alice@example.com", "bob@example.com", "charlie@example.com",
            "dave@example.com", "eve@example.com", "frank@example.com",
            "grace@example.com", "heidi@example.com", "ivan@example.com",
            "judy@example.com"
        };
        System.out.println("System started...");
        // 1. Create a fixed thread pool with 3 threads
        ExecutorService executor = Executors.newFixedThreadPool(3);
        for (String email : emails) {
            // 2. Submit the task using a lambda expression
            executor.submit(() -> {
                System.out.println("Sending email to " + email + "...");
                try {
                    // Simulate network delay
                    Thread.sleep(1000); 
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                }
                System.out.println("Email sent to " + email + "!");
            });
        }
        // 3. Shut down the executor to reclaim resources
        executor.shutdown();
        System.out.println("All tasks submitted. Main thread continues...");
    }
}