Mail App - Discourse Mails unreadable due to HTML priority

Hey,

I run a Nextcloud (Version 29.0.4) on a LCMP (Linux, Caddy, MySQL/MariaDB, PHP) stack on a Debian 12 server and found following possible bug.

Mails from a Discourse instance are displayed in their HTML version unreadable and the Mail app defaults to displaying the HTML version of said app.

On dark mode:

On light mode:

Noted: This can be also a bug on the side of Discourse. Other mail applications and webmailer like SOGo are displaying the mails correctly.

Example SOGo:

Added bug report: Github nextcloud/mail #9936