Scanning Existing Users' Email Addresses

The following code lists email address that did not pass validation and deletes them.

<?php
add_action( 'wp_ajax_validate-users', 'validate_users_email' );

function validate_users_email() {
    if ( ! current_user_can( 'delete_users' ) ) {
        echo 'Permission denied'; die;
    }
    $users = get_users( 'role=subscriber' );
    foreach( $users as $user ) {
        if ( ! is_email( $user->user_email ) ) {
            echo $user->user_login . ' ' . $user->user_email . '<br>';
            wp_delete_user( $user->ID );
        }
    }
    die;
}

Add this code to the functions.php file, login as an administrator and navigate to the following URL:

https://yoursite.com/wp-admin/admin-ajax.php?action=validate-users