Validate smtp server credentials using java without actually sending mail

Question

To verify smtp server credentials shall I use transport.connect()?

Session session = Session.getInstance(properties,authenticator);

 Transport tr=session.getTransport("smtp");

 tr.connect();

Is it correct method to check smtp server credentials?

Answer 1

This question: 'Verify mail server connection programmatically in ColdFusion' has a java solution as part of the accepted answer:

int port = 587;
String host = "smtp.gmail.com";
String user = "username@gmail.com";
String pwd = "email password";

try {
    Properties props = new Properties();
    // required for gmail 
    props.put("mail.smtp.starttls.enable","true");
    props.put("mail.smtp.auth", "true");
    // or use getDefaultInstance instance if desired...
    Session session = Session.getInstance(props, null);
    Transport transport = session.getTransport("smtp");
    transport.connect(host, port, user, pwd);
    transport.close();
    System.out.println("success");
 } 
 catch(AuthenticationFailedException e) {
       System.out.println("AuthenticationFailedException - for authentication failures");
       e.printStackTrace();
 }
 catch(MessagingException e) {
       System.out.println("for other failures");
       e.printStackTrace();
 }

Answer 2

public boolean confirmSMTP(String host, String port, String username, String password, String auth, String enctype) {
    boolean result = false;
    try {
        Properties props = new Properties();
        if (auth.equals(true)) {
            props.setProperty("mail.smtp.auth", "true"); 
        } else { 
            props.setProperty("mail.smtp.auth", "false"); 
        }
        if (enctype.endsWith("TLS")) {
            props.setProperty("mail.smtp.starttls.enable", "true");
        } else if (enctype.endsWith("SSL")) {
            props.setProperty("mail.smtp.startssl.enable", "true");
        }
        Session session = Session.getInstance(props, null);
        Transport transport = session.getTransport("smtp");
        int portint = Integer.parseInt(port);
        transport.connect(host, portint, username, password);
        transport.close();
        result = true;

    } catch(AuthenticationFailedException e) {
        Logging.addMsg(e.toString(), "SMTP: Authentication Failed", false, true);

    } catch(MessagingException e) {
        Logging.addMsg(e.toString(), "SMTP: Messaging Exception Occurred", false, true);
    } catch (Exception e) {
        Logging.addMsg(e.toString(), "SMTP: Unknown Exception", false, true);
    }

    return result;
}