Hopefully you know that Google keeps track of everything you have searched for. Ever. Anyway, the part that people probably don’t know as much about is how individual sites track you. One way a site can track you is by tagging you when you click through on an e-mail they send you – the focus of this post. Think of tags as dated stamps in your passport book. Interestingly enough, some of this tagging can be easily found in the address bar of your browser.
When you see something in the address bar that looks like emid=584783 that is telling the website that your internal – meaning site specific- e-mail address ID is 584783. This value is unique to a single e-mail address. Each e-mail sent to that e-mail address will have their unique emid attached to all links in the e-mail. This also allows a site to build a history of that e-mail address – not only for activity, but for response rate as well. Now every time you click through an e-mail for that site they have more history. Note that larger sites rarely look at individual behavior but instead classify a behavior and then analyze that group. Still, the information is there.
In addition to an e-mail ID, there is usually a campaign variable such as cid=Sep08FreeShipping. This allows the site to report on everything with Sep08FreeShipping stored in the cid variable. All of this information is contained within the link that you click from the e-mail. If you get the e-mail and directly load their site, not through the e-mail, the activity will not be tracked because in a direct load no value would have been assigned to cid.
These variables do not have to remain in the web address the entire time. They are stored in the background after the initial click. So when you no longer see emid or cid in the address bar, but originally arrived at the site through the e-mail, you and your activity is still being tracked.
Look for at least one more installment of how you are tracked. There I will focus more on how a site tracks internal campaigns. Hope this helped give some people a better understanding of how websites track you.