@KorespondentAdaif I understand your question correctly, you are talking about something like a CalDAV connector.Which btw is already used by Thunderbird/Lightning to connect to NextCloud/OwnCloud and lots of other calendar/task providers.If my googl...
What about:setting a folder to unthreadedclicking on the small icon in the right top of the message list pane (the one where you can choose which columns you want to see)hovering over "Apply current view to..."hovering over "Folder and its children.....
