Edit in JSFiddle

<input type="email" class="input-check-email">
<div id="result-check">

</div>

// email check function
function email_check( email ) {    
    var regex=/([\w-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([\w-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$/;
    return (email != '' && email != 'undefined' && regex.test(email)); 
}

// check when email input lost foucus
$(".input-check-email").blur(function(){
  var email = $(this).val();

  // if value is empty then exit
  if( email == '' || email == 'undefined') return;

  // valid check
  if(! email_check(email) ) {
  	$("#result-check").text('Not valid email.');
    $(this).focus();
    return false;
  }
  else {
  	$("#result-check").text('Email address test OK.');
  }
});