With old lists, unresponsive lists or third party, is there any other alternative to cleaning a list before mailing to it?

Unfortunately, no. A list no more than 2 months old MUST be hygiened.

Why? Because bounces can generate fast, domains can be bought and spam fighters can infiltrate your list if not kept massaged.

Bottom line is, you must mail to your list at least twice a month to avoid blacklists or an ESP to pause your campaign.