In order to link to a previous email message, you'll need to first find the "permalink", or permanent URL to that previous email.
- Go to Reports -> Email Tracking.
- Select the previous email you'd like to link to and open the report.
- You'll see an item on the Summary screen called "Permalink." Copy that link to your clipboard or to notepad for future reference.
- Take the link you just copied, and insert it into a message like any other link.