I think he means that a lot of pure-spam emails include an unsubscribe link that actually proves to the spammer that they've reached a live person, and then the

I think he means that a lot of pure-spam emails include an unsubscribe link that actually proves to the spammer that they've reached a live person, and then they'll resell your address to everyone. It can be difficult to tell if it's a fake UniversalBankCo email or a real one, even if you are a UniversalBankCo customer.