I am brand-new to Thunderbird (91.4.0), having been a Windows Live Mail user for longer than I care to remember. I tried various strategies in an attempt to import my Storage Folders from WLM (as indicated in several posts on this forum) but nothing worked. I then remembered that my favourite mail archive package - 'Mailstore Home' (www.mailstorehome.com) - had an 'export to Thunderbird' function so I used Mailstore Home to 'suck' my WLM Storage Folders into a Mailstore Home archive and then (again, using Mailstore Home) 'pushed' them into Thunderbird. At the time of writing this appears to have been 100% successful. I hope that maybe this is helpful to someone else.