Disable submit function when error message appears

How do I "lock" or "disable" the form button when the error message appears?

Input

<input style="height:24px;" name="email" id="email" title="<?php echo Mage::helper('core')->quoteEscape(Mage::helper('contacts')->__('Email')) ?>" class="input-text required-entry validate-email" autocapitalize="off" autocorrect="off" spellcheck="false" />

                   <p style="color: #ee001c" id="para" name="para" class="ok"></p>

jQuery

   $j(document).ready(function() {
    $j("#email").focus(function() {}).blur(function() { 
        $j("contactForm").submit(function () { return false; });
        //atribuindo o valor do campo
        var sEmail  = $j("#email").val();
        // filtros
        var emailFilter=/^.+@.+\..{2,}$/;
        var illegalChars= /[\(\)\<\>\,\;\:\\/\"\[\]]/
        // condição
        if(!(emailFilter.test(sEmail))||sEmail.match(illegalChars)){
            $j("#para").show().removeClass("ok").addClass("erro")
            .text('Informe um endereço de email válido. Por exemplo, [email protected].');
        }else{
        }
    });
    $j('#email').focus(function(){
        $j("#para").hide();
    });
   });

Solution

        function validateEmail(email) {
        var re = /^(([^<>()[\]\.,;:\s@\"]+(\.[^<>()[\]\.,;:\s@\"]+)*)|(\".+\"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;
              return re.test(email);
            }

            function validate() {
              $j("#para").text("");
              var email = $j("#email").val();
              if (validateEmail(email)) {
            return true;
              } else {
            $j("#para").text("Informe um endereço de email válido. Por exemplo, [email protected].");
            return false;
              }

            }

            $j(".validate").bind("blur", validate);
            $j("#validate").bind("click", validate);