Java Smtp服务器向sslsocket发出starttls命令，但当STARTHANKE（）读取超时时

sslsocket总是在sslsocket.startHandshake（）时读取超时，那么我应该如何解决该问题

    public static Socket createSsl(Socket socket) throws IOException {
    SSLSocketFactory factory = (SSLSocketFactory) SSLSocketFactory.getDefault();
    SSLSocket sslsocket = (SSLSocket) (factory.createSocket(socket, socket
        .getInetAddress().getHostAddress(), socket.getPort(), true));
    sslsocket.setUseClientMode(false);
    sslsocket.startHandshake();
    return sslsocket;
  }