Junk Mail Databases

I would love to be able to delve into how information passes amongst mailing lists and junk mailers. I moved in to my current address a little less than a year ago. Obviously my parent's have never lived here nor used this address. A few months after moving in I got a few messages addressed to my dad. Now today I get an add addressed to my mom. I just wish I could figure out where and how the databases have connected my parent's to this address. It would be an interesting trail I assume.