I have an unwritten and entirely one-way rule with companies sending me emails. It’s very simple one: Allow me to unsubscribe from whatever list i am on in a single click from the email, or i will mark you as spam in Gmail and report you as spam via SpamCop.
That’s it. Companies are getting too comfortable with spamming us, so hitting them with a reputational hit is always a small (and perhaps in the big picture) but important go-fuck-yourself card you can play.