Block new user registration by domain

block-user-registration-by-domain.php

<?php

/**
 * Block User Registration by Domain
 *
 * Plugin Name: Block User Registration by Domain
 * Plugin URI: https://gist.github.com/afragen/178e9bb282cb95c82ac6ade5331e4ee5
 * Description: Block user registrations from specific email domains.
 * Version: 0.5.2
 * Author: Andy Fragen
 * Author URI: https://thefragens.com
 * License: MIT
 * Requires at least: 6.6
 * Requires PHP: 8.2
 * Gist Plugin URI: https://gist.github.com/afragen/178e9bb282cb95c82ac6ade5331e4ee5
 * Text Domain: block-user-registration-by-domain
 */

namespace Fragen\Block_User_Registration_By_Domain;

use WP_Error;

// Exit if accessed directly.
if (! defined('WPINC')) {
    die;
}

/**
 * Bootstrap.
 *
 * @return void
 */
function bootstrap(): void {
    add_filter('registration_errors', __NAMESPACE__ . '\\block_user_registration_by_domain', 10, 3);
}

/**
 * Check and block user registration by email domain.
 *
 * @param WP_Error $errors               A WP_Error object containing any errors encountered
 *                                       during registration.
 * @param string   $sanitized_user_login User's username after it has been sanitized.
 * @param string   $user_email           User's email.
 *
 * @return WP_Error
 */
function block_user_registration_by_domain($errors, $sanitized_user_login, $user_email): WP_Error {
    // Add more domains as needed.
    $blocked_domains = [
        'socialpave.com',
        'gemmasmith.co.uk',
    ];

    $email_domain = substr(strrchr($user_email, "@"), 1);

    foreach ($blocked_domains as $blocked) {
        if (str_ends_with($email_domain, $blocked)) {
            $errors->add('domain_blocked', __('Registrations from your email domain are not allowed.', 'block-user-registration-by-domain'));
            error_log( "Blocked user registration attempt from email domain: $email_domain" );
            break;
        }
    }

    return $errors;
}

bootstrap();