Function to verify if an email exists inside a Google Spreadsheet

VN_VERIFY_EMAIL.gs

/**
 * Verify that the provided email is well recognized by the MX server.
 *
 * @param {string} token : The API token bought at https://voilanorbert.com
 * @param {string} email : The email to verify
 *
 * @return Boolean as 1/0 if it exists or an error code (starting with "ERR-{code}")
 *
 * @customfunction
 */
function VN_VERIFY_EMAIL(token, email) {
  if (!token)    return "Please provide a token.";
  if (!email) return "Please provide an email.";
  
  var request = UrlFetchApp.fetch("https://www.voilanorbert.com/api/v2/verify", {
    'method': 'post',
    'muteHttpExceptions': true,
    'payload': {
      'token': token,
      'email': email
    }
  });
  
  var objRequest = Utilities.jsonParse(request.getContentText()),
      response = null;
  
  switch(request.getResponseCode()) {
    case 204:
      response = "1";
      break;
    case 404:
      response = "0";
      break;
    default:
      if (objRequest.code) {
        response = 'ERR-' + objRequest.code + ' : ' + objRequest.error;
        break;
      }
      response = 'ERR-' + objRequest.error;
  }
  
  return response;
}