Here are instructions for enabling open-rate tracking in your CCtoMany list:
Include this image in your HTML, usually at the bottom. You can include this image in your template file so all new messages have it automatically.
When properly included, the image will look like this (you will probably want to center it):
As each recipient's message is built, that link gets converted to a unique encoded URL which is then used to track each individual open event. So DO NOT copy the tracking image link from a message you've received! That image is linked to ONLY your own email address.