Among other things, they're using Criteo Email, which can supposedly identify an e-mail address for up to 30% of a site's unregistered traffic.

http://www.criteo.com/what-we-do/products/

You'll find that, along with a dozen other marketing/tracking related products, by observing all the JavaScript tags the site loads through your browser's network inspector. You won't find some of them in the HTML source because they're using tag managers to inject additional script tags into the page after it's loaded.