title: Multiple ESP8266 subscribe to one RPI 3
body: <p>i have problem to subscribe 2 (and more) ESP8266 to one RPi3 broker.
  I used:</p>
  
  <pre><code>import paho.mqtt.client as mqtt
  import datetime
  
  mqtt_topics = ["esp8266-1", "esp8266-2"]
  
  def on_connect(client, userdata, flags, rc):
      print("Connected with result code "+str(rc))
  
      for topic in mqtt_topics:
       client.subscribe(topic)
  
  def on_message(client, userdata, msg):
      print(datetime.datetime.now())
          print(str(msg.topic)+" "+str(msg.payload))
  
  client = mqtt.Client()
  client.on_connect = on_connect
  client.connect('localhost', 1883, 60)
  
  try:
      for topic in mqtt_topics:
          client.on_message = on_message
      client.loop_forever()
  except KeyboardInterrupt:
          print("CTRL-C: Terminating program.")
  </code></pre>
  
  <p>It works but ony to 1 esp.
  If i connect esp8266-1 it checks it values, then i connect esp8266-2 to have its values and esp8266-1 is no longer available (even if i turn of esp8266-2).</p>
  
  <p>How to subscribe both esp8266?
  I only can have one of them at time.</p>