I think I have seen the answer to this question before, but cannot find it now when I need it. So I ask here to see if anyone knows, and so that others can see the answer beside me.
Quote from the manual:
"- in Body Source you can find this line:
<p> <img border="0" height="1" src="http://www.site.com/email_open.php?eid={eid}" width="1" /> </p>
This line is added by default (even if you delete it) and used to track email statistics for Opened column. Please keep in mind if you wish to gather stats for other columns like Clicked, Orders (#), Orders ($) you should add a special parameter to the URL &eid={eid}."
What is the "special parameter" that is to be added?
