They probably bought a list from someone that compiled the appropriate demographic targets one way or another. If you shopped at Lowes, HD, et al and they have your email they may have sold that basic info - your email that shopped at a home center - to an aggregator, then on. If you are into DIY, you might like my hinges kinda thing. There are also programs that do "scraping", running through web sites and forums hunting email type address. Hence the "bob ACK dontsendmenodamnspam DIRT com" type postings trying to throw off the scrapers.
Unsolicited email here gets deleted. Period, I don't even open it. Only email from companies I've actually done business with. Even then, proceed with caution. Received and email at work this morning about "a broken link on your web site". I'm not the site admin but my name is connected to the school domain. Addressed by name , the link in the email was a valid link to one of our sites but a "mouse over" of the link revealed the hidden re-direct. Sorry, no deal.