Landing page creating duplicate contact

We are trying to use a landing page sent to a contact to append that contact’s custom fields. (Additional data collection). When the contact fills out the landing page, a duplicate contact is created if there is any variance in the capitalization of their email address. Is there an easier way to achieve the same results?

I was unable to create a duplicate record by changing the capitalization of the email address on my landing page. But, here is a script you can insert in the header that will automatically change the email address field to a lower case as the user types.
<script src=""></script><script>$(document).ready(function(){ $("#email").on('change keyup paste',function(){ $(this).val($(this).val().toLowerCase()); }) })</script>