When an eTrigue email is sent, all of the links in the email, including the opt-out link, are coded to be specific to the original recipient. This is partly how eTrigue knows which prospect in your DemandCenter database is visiting the email -- resulting in the recipient to be tracked under the appropriate prospect record.
If you receive a forwarded eTrigue email from an email client, like Microsoft Outlook, the coded links do not change. So, when you click on the links in the email, you will be identified as the original recipient. As a result, any future activity that you generate will be tracked under that recipient's prospect record. Similarly, when you submit an eTrigue-enabled form under an email address that is not your own, your ongoing activity would be tracked under the prospect record that matched the submitted email address.
If you find yourself cookied under a prospect that is not your own, clearing your browser cookies will remedy the situation. Please note that if you are using multiple web browsers, you may need to clear the cookies for each browser to ensure that they did not retain cookies that were coded for someone else.