MQTT client subscribed, messages received but the relay is not triggered

Using Arduino Programming Questions
1

Hi everyone, I'm experimenting with the PubSubClient library for the MQTT protocol.
I started from the example sketch and added three simple instructions to turn on a relay connected to PIN 12 when a message is received. From the serial monitor I can see that the client is correctly subscribed to the topic and it is receiving all the messages, however the relay does not turn on. I used this simple script

void setup() {
  pinMode(12, OUTPUT);
}

void loop() {
  digitalWrite(12, HIGH);  
  delay(3000);                      
  digitalWrite(12, LOW);   
  delay(7000);                    
}

to check if everything is wired correctly and it works. Can you help me in understanding what I am doing wrong? here is the code that I'm executing:

#include <SPI.h>
#include <Ethernet.h>
#include <PubSubClient.h>

const int MY_PIN = 12;
// Update these with values suitable for your network.
byte mac[]    = {  0xDE, 0xED, 0xBA, 0xFE, 0xFE, 0xED };
IPAddress ip(192, 168, 1, 77);
IPAddress server(192, 168, 1, 248);

void callback(char* topic, byte* payload, unsigned int length) {
  Serial.print("Message arrived [");
  Serial.print(topic);
  Serial.print("] ");
  for (int i=0;i<length;i++) {
    Serial.print((char)payload[i]);
  }
  digitalWrite(MY_PIN, HIGH);  
  delay(5000);                      
  digitalWrite(MY_PIN, LOW); 
  Serial.println("END CALLBACK");
}

EthernetClient ethClient;
PubSubClient client(ethClient);

void reconnect() {
  // Loop until we're reconnected
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    // Attempt to connect
    if (client.connect("arduinoClient")) {
      Serial.println("connected");
      // Once connected, publish an announcement...
      client.publish("outTopic","hello world");
      // ... and resubscribe
      client.subscribe("/hello");
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      // Wait 5 seconds before retrying
      delay(5000);
    }
  }
}

void setup()
{
  Serial.begin(9600);
  pinMode(MY_PIN, OUTPUT);
  client.setServer(server, 1883);
  client.setCallback(callback);

  Ethernet.begin(mac, ip);
  // Allow the hardware to sort itself out
  delay(1500);
}

void loop()
{
  if (!client.connected()) {
    reconnect();
  }
  client.loop();
}
2

Did the example sketch work before editing?