WordPress + MailOdds

// 1. Upload the 'mailodds' folder to /wp-content/plugins/
// 2. Activate via Plugins menu
// 3. Go to Settings > MailOdds and enter your API key
// 4. Enable the form integrations you need:
//    - WordPress Registration
//    - WooCommerce (registration + checkout)
//    - WPForms
//    - Gravity Forms
//    - Contact Form 7

// That's it! The plugin handles caching, timeouts, and error handling.

// functions.php - Manual integration (if not using the plugin)
// Validates email on registration with caching and fail-open timeout

add_action('registration_errors', function($errors, $sanitized_user_login, $user_email) {
    // Skip if API key not defined
    if (!defined('MAILODDS_API_KEY')) {
        return $errors;
    }

    // Check transient cache (24h TTL)
    $cache_key = 'mailodds_' . substr(hash('sha256', strtolower($user_email)), 0, 16);
    $cached = get_transient($cache_key);

    if (false === $cached) {
        $response = wp_remote_post('https://api.mailodds.com/v1/validate', [
            'headers' => [
                'Authorization' => 'Bearer ' . MAILODDS_API_KEY,
                'Content-Type'  => 'application/json',
            ],
            'body'    => json_encode(['email' => $user_email]),
            'timeout' => 5,
        ]);

        // Fail-open: if API unreachable, allow registration
        if (is_wp_error($response)) {
            return $errors;
        }

        $cached = json_decode(wp_remote_retrieve_body($response), true);
        if (isset($cached['result'])) {
            $cached = $cached['result'];
        }

        // Cache for 24 hours
        set_transient($cache_key, $cached, DAY_IN_SECONDS);
    }

    $action = isset($cached['action']) ? $cached['action'] : '';

    if ('reject' === $action) {
        $errors->add('invalid_email',
            'Error: This email address could not be verified.');
    }

    return $errors;
}, 10, 3);

// WooCommerce checkout validation (included in the plugin)
// Also validates on WooCommerce My Account registration

add_action('woocommerce_after_checkout_validation', function($data, $errors) {
    $email = isset($data['billing_email']) ? $data['billing_email'] : '';
    if (empty($email) || !defined('MAILODDS_API_KEY')) {
        return;
    }

    $response = wp_remote_post('https://api.mailodds.com/v1/validate', [
        'headers' => [
            'Authorization' => 'Bearer ' . MAILODDS_API_KEY,
            'Content-Type'  => 'application/json',
        ],
        'body'    => json_encode(['email' => $email]),
        'timeout' => 5,
    ]);

    if (is_wp_error($response)) {
        return; // Fail-open
    }

    $body = json_decode(wp_remote_retrieve_body($response), true);
    $result = isset($body['result']) ? $body['result'] : $body;

    if (isset($result['action']) && 'reject' === $result['action']) {
        $errors->add('validation',
            'This email address could not be verified. Please use a different email.');
    }
}, 10, 2);

# WP-CLI commands (included in the plugin)

# Validate a single email
wp mailodds validate user@example.com

# Validate with JSON output
wp mailodds validate user@example.com --format=json

# Bulk validate all unvalidated WordPress users
wp mailodds bulk

# Bulk validate with batch size and limit
wp mailodds bulk --batch=100 --limit=500

# Show plugin status and stats
wp mailodds status