function validate(form_id,email) {

   var reg = /^([A-Za-z0-9_\-\.])+\@([A-Za-z0-9_\-\.])+\.([A-Za-z]{2,4})$/;
   var address = document.forms[form_id].elements[email].value;
   
   if(reg.test(address) == false) {
      
      
      
      alert('Nieprawidłowy adres email');
      return false;
  
   }
}