At this time, it's not possible to send plain text emails with Jilt. You could use our HTML editor to create very basic HTML emails instead.
To do so, you can follow along below in the email editor:
Step 1: General set-up
While the content width container cannot be fully removed, you can adjust the content area width for the email up to 900px in the email editor's Settings tab:
Additionally, you could adjust the Content area alignment to "left" and the background colors to white (hex code #FFF) to help achieve a plain text look.
Step 2: Adding text
You can either add the text of your email using an HTML block (if you're familiar with HTML). Or, you can add the text with a Text block and remove the formatting in the Content tab (remove the padding, update text color to black (#000), etc.):