this:
{if !empty($email)} <input class="form-control" type="email" placeholder="{l s='[email protected]' d='Modules.Emailalerts.Shop'}"/> {/if}
change to:
<input class="form-control" type="email" placeholder="{l s='[email protected]' d='Modules.Emailalerts.Shop'}" value="{if !empty($email)}{$customer.email}{/if}"/>