Google Sheet script to verify email addresses automatically

Email-verifier.js

/**
 * A custom function that verifies an email ID
 *
 * @param {String} email ID
 * @return {Boolean} If the email ID is active
 * @customfunction
 */
function verifyEmail(email) {

  // Replace this with your Hunter.io API key
  var api_key = "<your api key>";
  var url = "https://api.hunter.io/v2/email-verifier?api_key=" + api_key;

  url += "&email=" + email;
  var response = UrlFetchApp.fetch(url);

  // Get response code
  var responseCode = response.getResponseCode();
  if (responseCode != 200) {
    return false;
  }
  
  // Parse response
  var json = response.getContentText();
 
  var data = JSON.parse(json);
  if (data["data"]["smtp_check"] != true) {
    return false;
  }
  return true;
}

function runVerifyEmail() {
  
  // Replace the col variable with the column in which your email IDs are stored
  // The status will be stored in the column to the right of the email column
  var row = 2;
  var col = 2;
  
  var sheet = SpreadsheetApp.getActiveSheet();
  
  var range = sheet.getRange(row,col);
  var lastRow = sheet.getMaxRows();
  var dataRange = sheet.getRange(row, col, lastRow, 3);
  
  // Fetch values for each row in the Range.
  var data = dataRange.getValues();
  for (var i = 0; i < data.length; i++) {
    var rowData = data[i];
    var email = rowData[0];  // First column
    var status = rowData[1]; // Second column

    if (status == "" && email != "") {  // Prevents sending duplicates
      
      response = verifyEmail(email);
      sheet.getRange(row + i, col + 1).setValue(response);

      // Make sure the cell is updated right away in case the script is interrupted
      SpreadsheetApp.flush();
    }
  } 
}