The newsletter used to be content-managed in wagtail.org until July 2023 (the latest page is https://wagtail.org/this-week-in-wagtail/issue-136/). Content display issues on Outlook prompted a move to a content template in Mailchimp.

Since https://github.com/wagtail/wagtail-newsletter is released, and it comes with MJML support, we can reimplement the current Mailchimp template as MJML, and move back to Wagtail-managed newsletters.