WHMCS blacklist check on ticket-form

<?php

if (!defined("WHMCS"))
    die("This file cannot be accessed directly");

use WHMCS\Database\Capsule;

add_hook('TicketOpenValidation', 1, function($vars) {
    $useremail = strtolower($vars['email']);

    if (!filter_var($useremail, FILTER_VALIDATE_EMAIL)) {
        return 'Invalid email format.';
    }

    $blocked = Capsule::table('tblticketspamfilters')
        ->where('type', 'sender')
        ->where('content', $useremail)
        ->exists();

    if ($blocked) {
        return 'Sorry, you cannot open a ticket.';
    }
});