If you use Google's Gmail then you can do the same type of thing using this nifty "+" sign technique. Simply add something extra to your email username to define which service or special offer you're signing up for to find out which websites are selling your email address to marketers. For example, if your normal email address is email@example.com and you're signing up for a competition with Little Goliath Ltd you would provide your email address as something like firstname.lastname@example.org. Thereafter, any emails arriving in your inbox to that very specific email address indicates who sold your email address to who.
We all hate spam, right? Well, so does Canada. They've recently passed a new law that will see them issue financial penalties of up to $1 million for individuals and $10 million to businesses that send email to people without their consent. And this law doesn't just apply to Canadians, it affects everyone. Here's what you need to know about the new Canadian anti-spam law. And here's the official documentation on the new law.