We send out all HTML emails as multipart mime, which includes both an HTML and text version. This method ensures that your list members receive your campaigns, even if their email client does not support HTML.
By default, the text version of your campaign will provide a link to the online view of your campaign. To edit or view the text version of your campaign, go to step 3 within the campaign creation process. Here, there will be 'Edit' and 'View' buttons for the 'TEXT VERSION'.