If you have a custom-designed MailChimp template, you can still enable MailChimp’s new drag and drop elements. Here’s how to do it.
In a stackoverflow post, someone had posted a link to the HTML code for one of Mailchimp’s default templates. Unfortunately, they hadn’t highlighted the exact code needed to make the editor work, but by some trial and error, I found that adding the code below to the template’s main content area will enable the drag and drop editor on your custom template.
<div mc:container="body_container" mccontainer="body_container"></div>
The mc:container tag will add the block editor section. The mccontainer tag (without the colon) is required for saving the content. These tags can be added to either a td or div tag (div tag shown above for context).
