Rated 5 out of 5 stars
Well done Marph. You've built a well crafted useful add-on.
If you have Thunderbird as your main email app and Joplin as your personal knowledgebase, make sure you install this add-on. It is pretty easy to install and configure. (You obviously have to connect it with Joplin so they can talk to each other.) And in Joplin, before you install this add-on, create a notebook that will act as an "INBOX" for your emails.
Once you have the "Joplin Export" add-on setup, you process emails in Thunderbird just like you did before, processing/deleting/filing the usual basic transient emails. When you come across any emails that impact a project or topic, simply click the [Joplin Export] button and those messages magically appear in Joplin, including attachments! What do you do next? Well... basically within the comfort of Joplin you integrate the content into your knowledgebase. Sweet!