Zen-Cart troubleshooting – I feel like making another post on zen-cart before I forget it.  More like a reminder for myself.   Here are simple changes without the need to install add-ons.  Tested on 1.5.4 myself.

File to change: /store/includes/templates/your_template/templates/tpl_contact_us_default.php

Before

<fieldset id=”contactUsForm”>

After

<fieldset id=”contactUsForm”>
<label class=”inputLabel” style=”display:none;” >Leave this empty:</label>
<input name=”url”  style=”display:none;” />

Another file to change:  file: /store/includes/modules/pages/contact_us/header.php

Before

// Send message
zen_mail($send_to_name, $send_to_email, EMAIL_SUBJECT, $text_message, $name, $email_address, $html_msg,’contact_us’);

After

// Send message
// if the url field is not set or set and is empty
if( !isset($_POST[‘url’]) || ((isset($_POST[‘url’]) && $_POST[‘url’] == ”))){
zen_mail($send_to_name, $send_to_email, EMAIL_SUBJECT, $text_message, $name, $email_address, $html_msg,’contact_us’);
}

Source Credit (post#13): https://www.zen-cart.com/showthread.php?93026-prevent-people-from-using-contact-us-for-spam/page2