Sometimes your address isn't maliciously being sold but is just leaked through incompetence. I worked for a company who's mailing list ended up being leaked to

Sometimes your address isn't maliciously being sold but is just leaked through incompetence. I worked for a company who's mailing list ended up being leaked to spammers. Our (otherwise seemingly legit) mailing service we used for our opt-in-only mailing list got breached. We got lots of irate customers (there are surprisingly many people who use catch-alls), the mailing list provider put up a blog post saying "they were investigating" with no followup, and suddenly month later they redesigned their blog and the old post was gone...