EmailService.java

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.InternetAddress;
import javax.mail.internet.MimeMessage;

public class EmailService {

    // port that javax.mail work with
    private static final String SMTP_HOST = "smtp.gmail.com";
    private static final String SMTP_PORT = "587";
    // auth things
    private static final String USERNAME = System.getenv("EMAIL_USERNAME");
    private static final String PASSWORD = System.getenv("EMAIL_PASSWORD");

    public static void sendEmail(String recipient, String subject, String body)
            throws MessagingException {

        // like headers for our work
        Properties props = new Properties();
        props.put("mail.smtp.host", SMTP_HOST);
        props.put("mail.smtp.port", SMTP_PORT);
        props.put("mail.smtp.auth", "true");
        props.put("mail.smtp.starttls.enable", "true");

        Session session = Session.getInstance(props, new javax.mail.Authenticator() {
            @Override
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(USERNAME, PASSWORD);
            }
        });

        Message msg = new MimeMessage(session);
        msg.setFrom(new InternetAddress(USERNAME));
        msg.setRecipients(Message.RecipientType.TO, InternetAddress.parse(recipient));
        msg.setSubject(subject);
        msg.setText(body);

        Transport.send(msg);
    }
}