You must be living in a different world than me. I regularly get spam even from large corporations, that I know I never signed up for anything for. I know it is actually them, because it's DKIM signed with their domain certificates. Walmart (which doesn't exist in my country), Unilever and tons or their brands.

Even a national division of Microsoft got hands on my email and decided to sign me up for invites to developer events (I know I hadn't signed up for it, because they didn't even use my name in the mails, which they certainly would have known if they had gotten it through any legitimate source).

I assume it's bullshit KPIs, or signup schemes. Some poor seller at Microsoft or Walmart who's ranked according to how many people sign up to the opt-out company promotions, and buys harvested addresses to juice their numbers.

I even got some very obvious fraud spam ("Your [expensive product] is waiting for you!", trying to get you to sign up as a "product tester" only paying $$$ per month) with full DKIM signatures from a site hosted at a Danish hosting provider, and Danish business info. You'd think this sort of thing gets shut down quickly, but nope. The only times I've tried to address this sort of thing through the proper channels (domain registrar's abuse accounts, etc.), I've only gotten markedly more spam.

At least DKIM signatures makes it easy to autodelete mail. No need to even go into the spam folder, I'm happy to forbid Walmart from communicating with me by mail forever.