function validar(formulario) {

if (formulario.email.value == "")
{
alert("You have to write Email.");
return false;
}
if(checkEmail(formulario.email)==false)
{
 return false;
}
document.forms['formulario'].submit();

}

    function checkEmail(valor) {
  if (/^\w+([\.-]?\w+)*@\w+([\.-]?\w+)*(\.\w{2,3})+$/.test(valor.value))
  {

   return true;
  } else {
     alert("Email: " + valor.value    + " is incorrect.") 
valor.focus();
   return (false);
  }
 }