Domain validation for e-mail in WooCommerce checkout an registration forms

Providing an invalid e-mail address is one of the most common mistakes people do when shopping online and WooCommerce is not an exception. It is a mistake so common, that at least 1 of the 100 people will make a typo in their e-mail address when filling out a checkout form.

WooCommerce still does not do a proper domain validation for e-mail addresses and that is one of the reasons why WooCommerce store owners often get calls from their customers about order not being placed. All it does is a basic check if the provided e-mail address is in a correct format. On top of that – this also allows malicious bots to place orders or register accounts with non-existant e-mail addresses.

Further down in this article you will find a ready to use solution on how to properly validate customer e-mail addresses on the WooCommerce Checkout and WooCommerce Registration forms (both WooCommerce Classic and WooCommerce Blocks checkout are supported!) – if you’re not into reading, you can jump straight to the solution.

How a proper e-mail validation should work:

1. Reduce the chance for user to enter an incorrect e-mail address – make the e-mail field larger, with large enough, easy-to-read text and contrasting colors so it is easy to spot typos.
2. Check the entered e-mail address against common syntax errors – make sure it is provided in a proper format (WooCommerce already does that so skip to next step)
3. Check the domain of entered e-mail address against whitelist of domain names used by common e-mail providers (e.g. gmail.com, outlook.com, yahoo.com and so on)
4. Check the domain of entered e-mail address against blacklist of domain names (e.g. example.com, gnail.com, gmai.com, gail.com, outloo.com and so on). This blacklist is important because for each known e-mail provider there are tons of similar domain names which are active and validity of the entered e-mail address can’t be ensured in other ways. An e-mail address may be valid, but if the domain is similar to a known e-mail provider – it is a high chance that the user has made a typo.
5. After the basic validation steps are done – check if the e-mail address domain is active by querying its DNS records. This is also very important when dealing with user made typos.

Code snippet: Additional e-mail validation for WooCommerce checkout and registration forms

Just place this code in your theme functions.php file or add it as a must-use plugin. This code snippet will do additional validation for the e-mail address input fields on WooCommerce checkout and registration forms by checking if a domain of the e-mail provider is valid (whitelist check, blacklist check and validation of domain DNS records).

This code snippet supports both: WooCommerce Classic Checkout and WooCommerce Blocks Checkout forms

//DoInWP - Function to check if e-mail address is valid and reachable
if(!function_exists('dwp_check_if_email_is_valid')) {
  function dwp_check_if_email_is_valid($email) {
      $email_precheck = !empty($email) && strpos($email, '@') !== false && filter_var($email, FILTER_VALIDATE_EMAIL);
      if($email_precheck === FALSE) {
          return false;
      }
      $email_domain = preg_replace('/^.+?@/', '', $email);
      $email_domains_whitelist = ['gmail.com', 'yahoo.com', 'outlook.com', 'icloud.com'];
      $email_domains_blacklist = ['gmai.com', 'gmeil.com', 
        'gmail.co', 'gmaii.com', 'gmailc.com', 'gmil.com', 'gmsil.com', 'gnail.com',
        'icloudl.com', 'yaho.com', 'example.com'];
      if(in_array($email_domain, $email_domains_whitelist)) {
          return true;
      }
      if(in_array($email_domain, $email_domains_blacklist) || (!checkdnsrr($email_domain.'.', 'MX') && !checkdnsrr($email_domain.'.', 'A'))){
          return false;
      } 
      return true;
  }
}

//DoInWP - E-mail Validation for WooCommerce Classic Checkout
add_action('woocommerce_checkout_process', function() {
    if(isset($_POST['billing_email']) && !dwp_check_if_email_is_valid($_POST['billing_email'])) {
        wc_add_notice( esc_html__( 'You entered an invalid or non-reachable e-mail address. Please check it and try again.', 'woocommerce' ), 'error' );
    } 
});

//DoInWP - E-mail Validation for WooCommerce Blocks Checkout
add_action('woocommerce_store_api_checkout_update_order_from_request', function($order, $request) {
    $email = $order->get_billing_email();
     if(!dwp_check_if_email_is_valid($email)) {
        throw new \Automattic\WooCommerce\StoreApi\Exceptions\RouteException(
                'woocommerce_rest_checkout_invalid_email_domain',
                esc_html__( 'You entered an invalid or non-reachable e-mail address. Please check it and try again.', 'woocommerce' ),
                400
        );
     }
}, 10, 2);


//DoInWP - E-mail Validation on WooCommerce Registration Form
add_filter('woocommerce_registration_errors', function($errors, $username, $email) {
     if(empty($email)) {
        return $errors;
    }
    if(!dwp_check_if_email_is_valid($email)) {
            $errors->add(
                'woocommerce_registration_error_invalid_email_domain',
                esc_html__('You entered an invalid or non-reachable e-mail address. Please check it and try again.', 'woocommerce'));
    }
    return $errors;            
}, 10, 3);