I have used Thunderbird since its inception and keep all my mail history since '07 well organized for each year (archived in local folders for older material and many separate subfolders for various email categories (utilities, credit cards, kids school etc.). I originally attempted Apple's Migration program for transfer but lost all my categories in the process. I went back and made sure I had identical versions of Thunderbird 140.4 on each computer (couldn't get the newest version on my old computer). I followed the directions in the Thunderbird support pages to a 'T' to transfer my profile from the old mac to the new one. The only variation in the directions was the inclusion of the profile within the path of <Mac HD-Users-myname-Library-Thunderbird-Profiles> but the location was the same for both computers. When I returned to my old computer the final time I also lost all of it's organization subfolders. Any help you could offer would be greatly appreciated, because to have to resort what now looks like 1000's of unread emails in my inbox would be impossible to say the least. Thanks in advance for your time and attention. Sincerely, Jack Milne