Validating SMTP credentials for JavaMail without actually sending email

Question

Is there a way to verify the user credentials of the SMTP server without sending email or connecting to POP / IMAP. Some of the code I tried to write fails. You can find what is missing there.

Do not worry about Email / Password. I know it there.

NOTE. If you are trying to execute code. Case 1 must be transmitted when providing the correct credentials. If this fails, someone changed the password. You must use a different email address.

import java.util.Properties;

import javax.mail.Authenticator;
import javax.mail.MessagingException;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Transport;

public class EmailTest {

 public static void main(String[] args) {
  EmailHelper eh = new EmailHelper();

  /* GMail Setting for SMTP using STARTTLS */
  String name = "AAA";
  String email = "[e-mail]";
  String smtpHost = "smtp.gmail.com";
  String serverPort = "587";
  String requireAuth = "true";
  String dontuseAuth = "false";
  String userName = email; // same as username for GMAIL
  String password = "zaq12wsx";
  String incorrectPassword = "someRandomPassword";
  String enableSTARTTLS = "true";
  String dontenableSTARTTLS = "false";

  try {
   /* only valid case */
   eh.sendMail(name, email, smtpHost, serverPort, requireAuth,
     userName, password, enableSTARTTLS);
   System.out.println("Case 1 Passed");

   /* should fail since starttls is required for GMAIL. */
   eh.sendMail(name, email, smtpHost, serverPort, requireAuth,
     userName, password, dontenableSTARTTLS);
   System.out.println("Case 2 Passed");

   /* should fail since GMAIL requires authentication */
   eh.sendMail(name, email, smtpHost, serverPort, dontuseAuth, "", "",
     dontenableSTARTTLS);
   System.out.println("Case 3 Passed");

   /* should fail. password is incorrect and starttls is not enabled */
   eh.sendMail(name, email, smtpHost, serverPort, requireAuth,
     userName, incorrectPassword, dontenableSTARTTLS);
   System.out.println("Case 4 Passed");
  } catch (MessagingException e) {
   e.printStackTrace();
  }
 }

}

class EmailHelper {

 private Properties properties = null;
 private Authenticator authenticator = null;
 private Session session = null;

 public void sendMail(String name, String email, String smtpHost,
   String serverPort, String requireAuth, String userName,
   String password, String enableSTARTTLS) throws MessagingException {
  properties = System.getProperties();
  properties.put("mail.smtp.host", smtpHost);
  properties.put("mail.smtp.port", serverPort);
  properties.put("mail.smtp.starttls.enable", enableSTARTTLS);
  properties.put("mail.smtp.auth", requireAuth);
  properties.put("mail.smtp.timeout", 20000);

  authenticator = new SMTPAuthenticator(userName, password);

  session = Session.getInstance(properties, authenticator);

  // session.setDebug(true);

  Transport tr = session.getTransport("smtp");
  tr.connect();
  /*
   * do I need more than just connect? Since when i try to send email with
   * incorrect credentials it fails to do so. But I want to check
   * credentials without sending an email. Assume that POP3/IMAP username
   * is not same as the SMTP username, since that might be one of the
   * cases
   */
 }
}

class SMTPAuthenticator extends Authenticator {

 private String userName = null;
 private String password = null;

 public SMTPAuthenticator(String userName, String password) {
  this.userName = userName;
  this.password = password;

 }

 @Override
 public PasswordAuthentication getPasswordAuthentication() {
  return new PasswordAuthentication(userName, password);
 }
}

Answer 1

- SMTP. . "connect", "EHLO", . - , RFC. JavaMail "AUTH" , , , . ​​ , "STARTTLS" ( ), , , PLAIN . JavaMail "EHLO" "STARTTLS" .

, - true "mail.smtp.starttls.enable". JavaMail ( , 1.4.5) , "STARTTLS" , , ( ), , JavaMail, , "AUTH".