Can you then continue to track their path through the site, or only their entry page (page.php)? Most of the email service companies (like Constant Contact and Vertical Response) can tell you who clicked through which links in the email. But, they can't tell you where the visitor went after the landing page.

If you wanted to continue to track their path, would you have to attach the id to every link on each page within the site? Or is there something simpler that I'm missing? Thanks!