How to Show Emails as Appearing in a Thread in a Campaign

To have emails in a campaign appear as though they are in a thread: 

1. Clone the the first email in the thread (e.g. "Email follow up #1")

2. Rename the cloned email to create the second email in the thread (E.g. "Email Follow Up #2")

3. Within the second email in the thread, add the new email content above the previous email content

E.g. Inside "Email follow up #2":

You can repeat this process (cloning the previous email and adding new content) for every email in the thread.