RSForm PHP script to silently reject submission from spammers based on their email address

rsform-reject-joomla.php

/**
 * This script is used to silently reject submissions from spammers if you know their email addresses that they
 * put into your contact form.
 * This script checks if the user's email in the submitted form exists in your configured blacklist of email addresses.
 * The comparison is done case-insensitive.
 * If match is found, then such submission is rejected.
 * Rejected submissions are not saved into the database of RSForm and all notification emails are not sent.
 * After the rejected submission received, the user will be redirected to the same contact page
 * (or another page if you configure that) with a configurable message.
 * Usually such message should be a fake successfully received submission notification, so it does not look
 * suspicious to the spammer.
 * Tested with Joomla 3.10.9, RSForm 3.0.18, PHP 7.4.
 *
 * How to use:
 * 1) go to your form -> Form Properties -> PHP Scripts -> Script called on form process.
 * 2) put the code below into the "Script called on form process" textarea.
 * 3) change the configuration of the code according to our form.
 */

/**
 * Start of configuration, change the values below according to your form and needs
 */

//The field in RSForm for the email field
$fieldName = 'contact-email';
//List of user emails that are blacklisted and such submissions will be rejected, one per line
$blacklist = [
    '[email protected]',
    '[email protected]',
];
//Fake message to the user that the form has been submitted:
$fakeMessage = 'Thank you! Your form has been submitted';

//Redirect URL, usually you don't need to change that:
$redirectUrl = JRoute::_('index.php');

/**
 * End of configuration, please, don't change the code below
 */

$app = JFactory::getApplication();
if (isset($_POST['form'][$fieldName]) && in_array(mb_strtolower(trim($_POST['form'][$fieldName])), $blacklist)) {
    $app->enqueueMessage($fakeMessage);
    $app->redirect($redirectUrl);
}