function valid_email(email) {
var bad_char;
var bad_chars = " !#$%^&*()+|\=?/:,;";
 
      if (email == "") { 
			return false; 
		}
		
      for (i=0; i<bad_chars.length; i++) {		
      	bad_char=bad_chars.charAt(i)
	      if (email.indexOf(bad_char) != -1) {
	         return false;
	      }
      }
		
		if (email.indexOf("@") <= 0){
			return false;
		}
		
		 if (email.indexOf("@", email.indexOf("@")+1) != -1) { 
		 	return false; 
		}
		
		if (email.indexOf(".",email.indexOf("@")+1) == email.indexOf("@")+1) { // znak . zaraz po znaku @ w adresie email
   			 return false; 
		 }

		
		if (email.indexOf(".") <= 0){
			return false;
		}
		
      if((email.indexOf(".")+3) > email.length) { 
			return false; 
		} 

      return true
}