looking in to see responses
They have computers that randomly generate email addresses and they send out their “feelers” to these addresses “in the blind” by the millions because there’s virtually no cost in doing so. And if they get a reply, even if it’s an “Unsubscribe,” they know they’ve found a live one.
I never click unsubscribe unless it’s someone I knowingly have had transactions with, or it’s a return address I have verified as legit. I just put the address in the reject list in my local email client.