I don't know that there is one good answer. Different companies do it different ways--I've seen donation departments, customer service departments, consumer relation departments, community service departments, etc., etc., all handle this type of thing. I would call or e-mail first and get a person's name, if possible--if you can't get a name, then ask what department typically handles this. If you put down a department name that doesn't exist at that company, you significantly increase your risk that your letter goes to the circular file department!