java send email using apache commons net smtp timeout

The code:

public static void main(String[] args) {
    try {
        AuthenticatingSMTPClient c = new AuthenticatingSMTPClient();
        c.setDefaultTimeout(10000);
        c.connect("smtp.gmail.com", 587);
        c.ehlo("localhost");
        if (c.execTLS()) {
            c.auth(AuthenticatingSMTPClient.AUTH_METHOD.PLAIN, "xxx@gmail.com", "xxx");
            c.setSender("xxx@gmail.com");
            c.addRecipient("yyy@yahoo.com.hk");
            Writer w = c.sendMessageData();
            if (w != null) {
                SimpleSMTPHeader header = new SimpleSMTPHeader("xxx@gmail.com", "yyy@yahoo.com.hk", "Alert");
                w.write(header.toString());
                w.write("Alert test");
                w.close();
                if (!c.completePendingCommand()) {
                    throw new Exception("The email was failed to send. " + c.getReply() + c.getReplyString());
                }
            } else {
                throw new Exception("The email was failed to send." + c.getReply() + c.getReplyString());
            }
            c.addProtocolCommandListener(new PrintCommandListener(new PrintWriter(System.out), true));
        } else {
            throw new Exception("STARTTLS was not accepted " + c.getReply() + " " + c.getReplyString());
        }
        c.logout();
        c.disconnect();
    } catch (Exception ex) {
        System.err.println(ex.toString());
    }
}

The result:

run:
java.net.SocketTimeoutException: Read timed out
BUILD SUCCESSFUL (total time: 13 seconds)

Why above code is timeout? Is it blocked me to use smtp by gmail? I checked that my username and password are both correct. And I found the example from http://blog.dahanne.net/2013/06/17/sending-a-mail-in-java-and-android-with-apache-commons-net/ and https://github.com/caarmen/network-monitor/blob/master/networkmonitor/src/main/java/ca/rmen/android/networkmonitor/app/email/Emailer.java

Thanks!