Email notification for broken links for Joomla. Add to your templates error.php file.

joomla-email-404.php

<?php
// Check for a referer and if so send mail
if (isset($_SERVER["HTTP_REFERER"])){
    $sitename = "My Website";
    // Mail Settings
    $mailer = JFactory::getMailer();
    // Set sender as site default
    $config = JFactory::getConfig();
    $sender = array( 
        $config->get('config.mailfrom'),
        $config->get('config.fromname') );
    $mailer->setSender($sender);
    // Set recipient
    $recipient = '[email protected]';
    $mailer->addRecipient($recipient);
    // Mail body
    $body   = "404 page alert for " . $sitename . "\n\n The user was referred from " . $_SERVER["HTTP_REFERER"] . " \n\n They were trying to reach a page at " . JURI::base() . ltrim($_SERVER['REQUEST_URI'], '/');
    $subject = "404 Error Alert for " . $sitename;
    $mailer->setSubject($subject);
    $mailer->setBody($body);
    $send = $mailer->Send();
}
?>