public static ArrayList<String> readDomains(String filename){
        
        ArrayList<String> list = new ArrayList<>();
        
        try {
            BufferedReader reader = new BufferedReader(new FileReader(new File(filename)));
            while (true) {
                String mail = reader.readLine();
                if (mail == null) break;
                list.add(mail.split("@")[1].toLowerCase());
            }
            
        } catch (FileNotFoundException ex) {
            
        } catch (IOException ex) {
        }
        return list;
    }