This sample code is for Mailbox Notification Using Blynk App tutorial.

mailbox_notification.ino

#include <ESP8266_Lib.h>
#include <BlynkSimpleShieldEsp8266.h>

// You should get Auth Token in the Blynk App.
// Go to the Project Settings (nut icon).
char auth[] = "YourAuthToken";

// Your WiFi credentials.
// Set password to "" for open networks.
char ssid[] = "YourNetworkName";
char pass[] = "YourPassword";

// Hardware Serial on Mega, Leonardo, Micro...
//#define EspSerial Serial1

// or Software Serial on Uno, Nano...
#include <SoftwareSerial.h>
SoftwareSerial EspSerial(2, 3); // RX, TX

// Your ESP8266 baud rate:
#define ESP8266_BAUD 9600

ESP8266 wifi(&EspSerial);

int sensorPin = 7;   // Input pin for the IR sensor
int count = 0;       // Mail counter
String stringOne = "You got ";
String stringTwo;
String stringThree = " new mail.";
String message;
boolean prevState = false;


void setup()
{
  // Debug console
  Serial.begin(9600);

  delay(10);

  // Set ESP8266 baud rate
  EspSerial.begin(ESP8266_BAUD);
  delay(10);

  Blynk.begin(auth, wifi, ssid, pass);
}

void loop()
{
  Blynk.run();
  int  state = digitalRead(sensorPin);
  
  if ( state == LOW && prevState == true) {
    count++;
    stringTwo = count;
    message = stringOne + stringTwo + stringThree;
    Blynk.notify(message);
  }
  prevState = state;

}

BLYNK_WRITE(V1)
{
  count = 0;
}