Who's selling your email address?

Ever wonder which companies that you shop with are selling off your address? 

I used to be very paranoid about giving my email address to companies that I shopped with for fear that they would sell it off and I would start to get a ton of spam.  Like most people, I countered this by doing all of my shopping with a hotmail account.  Now I get tons of spam at home so I'm not quite as paranoid about giving out my address.  Still, I'm curious which companies are selling it off. 

This is a technique I've started to use to attempt to track the selling of my address.  A friend of mine did this in college with good results.  The downside of this technique is that you essentially need to have your own email server. 

Suppose your email address is your name (in my case jared).  Whenever you start shopping with company foo, create an additional email address named jared_foo@yourdomain.com  Only use that addres when shopping with foo.  Then all you need to do is add an Outlook Rule to filter out any messages that start with jared_ to a special folder.