How do I reinstate all archived emails into the folder pane ... the newer Thunderbird defaults to archiving and I've 'lost' a bunch of emails into the archive

<blockquote> the newer Thunderbird defaults to archiving </blockquote> Thunderbird does not auto-archive. It's something you'll have to trigger manually. <blockquote> I've 'lost' a bunch of emails into the archive </blockquote> Then I'd suggest you look at your Archive folder. To find out which folder has been designated as the Archive folder, check your account settings. https://support.mozilla.org/kb/archived-messages