Block registration from personal emails

This code is a variation of an mu-plugin Jason wrote to create an email whitelist here.

Create a document called s2-blacklist-email-domains.php and then copy and paste the following content into it:

<?php
add_filter('ws_plugin__s2member_pro_paypal_form_submission_validation_response', 'blacklist_email_domains', 10, 3);
add_filter('ws_plugin__s2member_pro_stripe_form_submission_validation_response', 'blacklist_email_domains', 10, 3);

function blacklist_email_domains($response, $form, $s)
{
    $blacklist = array(
		'gmail.com',
		'yahoo.com',
		'hotmail.com',
    );
    if(!$response) // No other errors produced by s2Member itself?
        if($form === 'registration' || !is_user_logged_in()) // Any new registration, or any new user completing checkout.
        {
            $domain = ''; // Initialize.
            if(isset($s['email']) && strpos((string)$s['email'], '@') !== FALSE)
                list(, $domain) = explode('@', (string)$s['email'], 2);

            if(!$domain || in_array(strtolower($domain), array_map('strtolower', $blacklist), TRUE))
                $response = array(
                    'error'    => TRUE, // This is an error.
                    'response' => _x('ERROR: You cannot use a personal email account.', 's2member-front', 's2member'),
                );
        }
    return $response; // Always return the filtered response.
}

Now upload that file to your /wp-content/mu-plugins folder. If you don’t have such a folder, create it. Apart from adding to or otherwise modifying the blacklist as desired, you should now be good to go.

I should add that you will need to be using Pro forms (whether Stripe or PayPal) for this to work.