The only major difference between the Import HTML and the Basic Editor pages is the initial pop-up you see when choosing the Import HTML page (Fig 1). 

Fig 1

When choosing a file to add to the Import HTML feature, it should be one of the following files types: 

• .HTM
• .HTML
• .ZIP

If your file is a .ZIP file, it needs to contain your source code (typically .HTML) along with associated images. 

After clicking on "Upload", you'll be directed to the Basic Editor with your uploaded code rendered in the New Basic Editor. 

To learn more about the new email builders, read the corresponding article:

• DND Builder
• Basic Editor