Stop spam emails from bots (without captcha)

A common problem many developers run into when creating a form that sends an email from a website while the form doesn't have a Captcha, is that the recipient usually receives a lot of spam emails from advertising bots.

An easy workaround for this issue consists of three parts:

1. Add a hidden input in your form

   <form id="your_form" action="some_action_if any">
      ...
      <input type="hidden"  id="some_unique_id" name="some_pretty_normal_name" value="value_to_remove" />
      ...
   </form>

2. When submitting the form, empty that hidden input

   /* This example is given with jQuery, though it can be implemented however you like. */
   
   $(document).ready(function() {
        $("#your_form").submit(function() {
            $("#some_unique_id").val('');
        });
   });

3. On the server side, send the email only if that hidden input is empty

   <?php
   ...
   if (!isset($_REQUEST['some_pretty_normal_name']) || empty($_REQUEST['some_pretty_normal_name'])) {
       ...
       mail($to, subject, $body, $headers);
   }
   ...
   ?>

And that's it !

This methods was checked on http://streamer.co.il after it was spammed by arbitrary ads and now they receive emails from real human beings :)