In my experience, you don't sign up for anything, but are automatically added to mailing lists against your will just for the sin of purchasing something. I never want to get emails from any company just because I purchased 1 item from them. Most people I know tell me they feel the same way, but instead of unsubscribing, they just mark it as spam and eventually it stops showing up in their inbox.

If I want emails from you, I will explicitly ask to be added to your mailing list. Anything else is spam as far as I'm concerned.

> just for the sin of purchasing something

Ah: prior commercial relationship. That's not spam, unless they ignore your unsubscribe request.

I hope you're not notifying the world that your preferred supplier of [X] is a spammer. I like to stay on good terms with my preferred suppliers.

illegal spam ⊆ spam

If I didn’t ask for it, it’s spam, regardless of whatever holes the US has punched in its definition to keep business owners happy.