API Java gratuita para enviar correos simples y basados en HTML

Maven Dependency

<dependency>
  <groupId>com.sun.mail</groupId>s;
  <artifactId>javax.mail</artifactId>
  <version>1.6.2</version>
</dependency>

Puede descargar la biblioteca directamente desde la página de GitHub.

¿Cómo enviar un correo de texto plano básico usando un servidor SMTP mediante la API Java?

import java.util.Properties;
import javax.mail.*;
import javax.mail.internet.*;

public class SimpleEmailSender {

    public static void main(String[] args) {
        // Sender's and recipient's email ID
        String from = "your.email@gmail.com";
        String to = "recipient.email@example.com";
        
        // SMTP server configuration (for Gmail)
        String host = "smtp.gmail.com";
        final String username = "your.email@gmail.com";
        final String password = "your-app-password"; // Use an App Password for Gmail

        // Setup mail server properties
        Properties properties = new Properties();
        properties.put("mail.smtp.auth", "true");
        properties.put("mail.smtp.starttls.enable", "true"); // Use TLS
        properties.put("mail.smtp.host", host);
        properties.put("mail.smtp.port", "587");

        // Get the Session object and pass username and password
        Session session = Session.getInstance(properties, new javax.mail.Authenticator() {
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(username, password);
            }
        });

        try {
            // Create a default MimeMessage object
            Message message = new MimeMessage(session);
            
            // Set From: header field
            message.setFrom(new InternetAddress(from));
            
            // Set To: header field
            message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(to));
            
            // Set Subject: header field
            message.setSubject("Hello from JavaMail API");
            
            // Set the actual message body
            message.setText("This is a test email sent programmatically using the JavaMail API.");

            // Send message
            Transport.send(message);
            System.out.println("Email sent successfully!");

        } catch (MessagingException e) {
            throw new RuntimeException(e);
        }
    }
}

¿Cómo buscar mensajes de un remitente específico dentro de aplicaciones Java?

Store store = session.getStore("imap");
store.connect("imap.example.com", username, password);

Folder inbox = store.getFolder("INBOX");
inbox.open(Folder.READ_ONLY);

// Search for messages from a specific sender
SearchTerm senderTerm = new FromStringTerm("alerts@example.com");
Message[] found = inbox.search(senderTerm);

for (Message m : found) {
    System.out.println("Subject: " + m.getSubject());
}

inbox.close(false);
store.close();