I got a newsletter from that I didn't remember subscribing to, possibly as a result of them being attached to a talk. (The first one appeared in my mailbox on October 26, so even I might remember something that recent.)

When I clicked the Unsubscribe link in the mail, the web page said "Fill out the form and we'll send you a link to edit your preferences."

So I went back to my email and reported them as and blocked them.

"Don't be that guy," but for corporations.