-
This is about to become even easier. Later this year, Google (and Apple and Yahoo) will be mandating one click unsubscribe links (rather than being taken to a website and made to log in/fill out a form to unsubscribe) on bulk email. I imagine features within those mailboxes will appear that will allow you to "unsubscribe from all bulk mail", or something similar. Click a button and Gmail will find all those links in your inbox and click them for you, sort of thing.
I solved a shitload of semi-spam from my Inbox by simply searching for "Unsubscribe" in my Inbox and slowly picking off stuff I didn't want to hear from ever again.
These are generally places that I've ordered from at some point in the past, but use that "existing business relationship" as an excuse to send endless offers. People like Uber, Saucony, Up & Running, Planet X, etc.