Sending emails over SMTP with TSL

The code posted below works fine for me to send an email over an STMP with SSL. Now the SMTP changed to TSL and i dont manage to send email with it. I tried several things like adding

props.put("mail.smtp.starttls.enable","true");

but it was no use.

The error code says:

"javax.mail.MessagingException: Could not connect to SMTP host: exch.studi.fhws.de, port: 587; nested exception is: javax.net.ssl.SSLException: Unrecognized SSL message, plaintext connection?"

Any ideas?

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

public class SendMail
{
String d_email = "...",
password = "...",
host = "...",
port = "25",
mailTo = "...",
mailSubject = "test",
mailText = "test";

public SendMail()
{
    Properties props = new Properties();
    props.put("mail.smtp.user", d_email);
    props.put("mail.smtp.host", host);
    props.put("mail.smtp.port", port);
    props.put("mail.smtp.starttls.enable","true");
    props.put("mail.smtp.auth", "true");
    props.put("mail.smtp.socketFactory.port", port);
    props.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
    props.put("mail.smtp.socketFactory.fallback", "false");

    SecurityManager security = System.getSecurityManager();

    try
    {
        Authenticator auth = new SMTPAuthenticator();
        Session session = Session.getInstance(props, auth);

        MimeMessage msg = new MimeMessage(session);
        msg.setText(mailText);
        msg.setSubject(mailSubject);
        msg.setFrom(new InternetAddress(d_email));
        msg.addRecipient(Message.RecipientType.TO, new InternetAddress(mailTo));
        Transport.send(msg);
    }
    catch (Exception mex)
    {
        mex.printStackTrace();
    }
}

public static void main(String[] args)
{
    TextClass tc = new TextClass();
}

private class SMTPAuthenticator extends javax.mail.Authenticator
{
    public PasswordAuthentication getPasswordAuthentication()
    {
        return new PasswordAuthentication(d_email, password);
    }
}
}

回答1:

The error message says you're connecting to port 587 - this is an SSL-enabled email port, which means the connection has to be SSL from the get-go. Your code is connecting via plaintext (e.g. plain port 25) and THEN attempting to start TLS. This won't work, as port 587 expects an SSL exchange immediately, not a "EHLO ... / STARTTLS" plaintext command set.

回答2:

Maybe this answer, talking about Exchange servers with SMTP ports disabled, is useful: https://stackoverflow.com/a/12631772/187148