You think spammers don't know what they're doing? They have all sorts of methods for harvesting addresses, ranging from scraping to data theft. They have figured out how to send a virtual shit ton of messages a day at almost no cost to themselves by developing and running botnets. They are on the cutting edge, and arguably, a major driver behind computer vision which they use for breaking captchas. They are a thorn in the side of every ISP, email provider and sys admin in the world. Years and too many man hours to count have been spent trying to stop spam, with a combination of technology and law. Still, the spammers manage to keep their enterprises humming along.

I think they have figured out how to sanitize email addresses.

SPAM has become a HUGE business. I'd guess they do have a pretty good idea about what they're doing.