Good evening, it is probably a trivial question but there is already an add-on for thunderbird to send mail directly to Joplin or is it not yet realized?
No, this does not exist yet.
But someone could use the web clipper code to get going. Instead of a web page, it just clips the body of the message, uses the subject as note title, ....
Tanks a lot
In the Apps category there are a few examples on how to do this: https://discourse.joplinapp.org/c/apps/11