java - Smtp 服务器向 sslsocket 发出 starttls 命令，但是当 startHandshake() 读取超时时

Question

    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;
  }

当 sslsocket.startHandshake() 时 sslsocket 总是读取超时，那么我应该怎么做才能解决这个问题呢？