If you have in-house designers, you can use the Upload ZIP file function to upload HTML newsletters which they save in .ZIP format.
Click Email > Create Email, and then click Upload ZIP file.
Once you have entered your email's properties in Step 1, you will be taken straight to the Upload from ZIP screen.
Follow these steps to import your newsletter in a ZIP file:
Once you have uploaded a ZIP file, a preview of the email will be shown in the preview panel.