import java.util.Arrays;
import java.util.Properties;
import java.util.function.Consumer;

import javax.mail.Authenticator;
import javax.mail.Folder;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.NoSuchProviderException;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Store;
import javax.mail.search.SearchTerm;

public class EmailTestMain {
    public static void main(String[] args) {
        String username = "[email protected]";
        String password = "Password";
        read(username, password, message -> {
            try {
                System.out.println(message.getSubject());
            } catch (MessagingException e) {

                e.printStackTrace();
            }
        }, Folder.READ_WRITE, null);
    }

    public static void read(final String username, final String password, Consumer<Message> messageConsumer,
            int folderAction, SearchTerm searchTerm) {
        final String host = "secureimap.t-online.de";
        Properties props = new Properties();

        props.setProperty("mail.imap.host", host);
        props.setProperty("mail.imap.user", username);
        props.setProperty("mail.imap.ssl.enable", "true");
        props.setProperty("mail.imap.ssl.tr ust", host); // JAVA truststore

        props.setProperty("mail.imap.socketFactory", "993");
        props.setProperty("mail.imap.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
        props.setProperty("mail.imap.socketFactory.fallback", "false");
        props.setProperty("mail.imap.port", "993");

        // Start SSL connection

        Session session = Session.getDefaultInstance(props, new Authenticator() {
            @Override
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(username, password);
            }
        });
        try (Store store = session.getStore("imap")) {
            store.connect(host, username, password);
            try (Folder emailFolder = store.getFolder("INBOX")) {
                emailFolder.open(folderAction);
                if (searchTerm != null) {
                    Arrays.stream(emailFolder.search(searchTerm)).forEach(messageConsumer::accept);
                } else {
                    Arrays.stream(emailFolder.getMessages()).forEach(messageConsumer::accept);
                }
            }
        } catch (NoSuchProviderException e) {
            e.printStackTrace();
        } catch (MessagingException e) {
            e.printStackTrace();
        }
    }
}

com.sun.mail.util.MailConnectException: Couldn't connect to host, port: secureimap.t-online.de, 993; timeout -1;
  nested exception is:
    java.net.ConnectException: Connection refused: connect
    at com.sun.mail.imap.IMAPStore.protocolConnect(IMAPStore.java:740)
    at javax.mail.Service.connect(Service.java:366)
    at javax.mail.Service.connect(Service.java:246)
    at de.bamberg.jugger.mail.EmailTestMain.read(EmailTestMain.java:55)
    at de.bamberg.jugger.mail.EmailTestMain.main(EmailTestMain.java:21)
Caused by: java.net.ConnectException: Connection refused: connect
    at java.net.DualStackPlainSocketImpl.connect0(Native Method)
    at java.net.DualStackPlainSocketImpl.socketConnect(Unknown Source)
    at java.net.AbstractPlainSocketImpl.doConnect(Unknown Source)
    at java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source)
    at java.net.AbstractPlainSocketImpl.connect(Unknown Source)
    at java.net.PlainSocketImpl.connect(Unknown Source)
    at java.net.SocksSocketImpl.connect(Unknown Source)
    at java.net.Socket.connect(Unknown Source)
    at java.net.Socket.connect(Unknown Source)
    at com.sun.mail.util.SocketFetcher.createSocket(SocketFetcher.java:353)
    at com.sun.mail.util.SocketFetcher.getSocket(SocketFetcher.java:218)
    at com.sun.mail.iap.Protocol.<init>(Protocol.java:134)
    at com.sun.mail.imap.protocol.IMAPProtocol.<init>(IMAPProtocol.java:131)
    at com.sun.mail.imap.IMAPStore.newIMAPProtocol(IMAPStore.java:763)
    at com.sun.mail.imap.IMAPStore.protocolConnect(IMAPStore.java:698)
    ... 4 more