Code-Snippets-Functions/Execute a function on a child site/Fluent Forms/ban-email-domains.txt

add_filter('fluentform/validate_input_item_input_email', function ($error, $field, $formData, $fields, $form) {
    /*
     * add your not accepted domains here
     * The mentioned domains will be failed to submit the form
     */
    $invalidDomains = ['gmail.com', 'hotmail.com', 'test.com']; // You may change here
    $errorMessage = 'The provided email domain is not accepted'; // You may change here

    $fieldName = $field['name'];
    if (empty($formData[$fieldName])) {
        return $error;
    }

    $valueArray = explode('@', $formData[$fieldName]);
    $inputDomain = array_pop($valueArray);

    if (in_array($inputDomain, $invalidDomains)) {
        return [$errorMessage];
    }
    return $error;
}, 10, 5);