function check_email(e) {
   ok = "1234567890qwertyuiop[]asdfghjklzxcvbnm.@-_QWERTYUIOPASDFGHJKLZXCVBNM";

   for(i=0; i < e.length ;i++){
     if(ok.indexOf(e.charAt(i))<0) return (false);
   } 

   if(document.images) {
     re = /(@.*@)|(\.\.)|(^\.)|(^@)|(@$)|(\.$)|(@\.)/;
     re_two = /^.+\@(\[?)[a-zA-Z0-9\-\.]+\.([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$/;
     if (!e.match(re) && e.match(re_two)) {
       return (-1);		
     } 
   }
   
   return false;
}

function submit_email(email) {
  if (!email) {
    alert('Please, input your email address');
    return false;
  } else if (!check_email(email)) {
    alert('Your email address has incorrect format');
    return false;
  }
  return true;
}