Paypal button not working in hotmail emails

Question

I'm having an issue with the paypal button code below not working when sent to a Hotmail address. It shows in the email source code and in the email message just fine. But when you click on it, it directs you to the paypal homepage.

This works fine in gmail and yahoo mail emails, but not Hotmail. The code below is what is used and how it appears in the emails.

Is there a reason why it's doing this, I can't find anything on it.

<form method="post" name="paypal_form" action="https://www.paypal.com/cgi-bin/webscr">
  <input type="hidden" name="business" value="email@email.com"/>
  <input type="hidden" name="invoice" value="NGQ2YWY1Nz000mZiYmEty1I2ZTMzZTcwOxxzMmI4Y="/>
  <input type="hidden" name="item_name" value="Acme Company [testes]"/>
  <input type="hidden" name="amount" value="4"/>
  <input type="hidden" name="rm" value="2"/>
  <input type="hidden" name="cmd" value="_xclick"/>
  <input type="hidden" name="currency_code" value="USD"/>
  <input type="hidden" name="notify_url" value="http://site.com/paypal.php?payment_status=ipn"/>
  <input type="hidden" name="cancel_return" value="http://site.com/paypal.php?payment_status=cancel"/>
  <input type="hidden" name="return" value="http://site.com/paypal.php?payment_status=success"/>
  <input type="hidden" name="upload" value="0"/>
  <input type="image" src="http://site.com/images/paypal_logo.png" width="197" height="48" class="paypal_button" name="submit" alt="Make payments with PayPal!" title="Make payments with PayPal!">
</form>

Answer 1

You should never use a <form> in emails -- never, ever. It cannot be trusted to work.

What is generating this <form> with POST variables for you, and why is it not using an <a> link with GET variables instead?