When working on your Email Campaign in the DND Builder, you can also view what a text-only version of the email looks like on the left-hand menu (Fig 1). 

Fig 1 

This will open the Text Version window (Fig 2). 

Fig 2 

If you click Regenerate, the text is regenerated to match what's in the HTML. 

If you click Finish, your changes to the Text Version will be changed. 

There will be an hover-over indicator next to the Text Version button on the side menu that will display text reminding you that the contents of the Text and HTML versions are different (Fig 3).

Fig 3 

If you make the HTML Version different from the Text Version and click Save, you'll now get a pop-up window stating that there are differences between the HTML and the Text versions (Fig 4). 

Fig 4

If you click on View Text Version Options, the Text Version window pops up so you can regenerate text to make it match the HTML Version. 

If you click on Save as is, you'll save the Email with the mismatched Text and HTML versions still intact.