I have an inbox with a few hundred emails. I use threading to keep the emails from each sender organized. I keep the threads closed until I need to read the ongoing conversation with that sender. Then I close it again. When I exit the inbox, Thunderbird used to keep the closed threads ... closed. Now, when I exit the inbox, and come back, the threaded conversations are ALL opened / exploded. I manually close the threads again, exit the inbox, come back, and they are again exploded into individual notes. They are still threaded, just that the conversations are expanded rather than compacted into the original note. What may have had an impact ? I created 2 subfolders below the inbox so that I could move the high volume of these threaded conversations into a "pending" status. BOTH of those subfolders behave correctly - threaded conversations remain either open or closed after exiting and then returning to the original folder. But the Inbox appears broken. I moved those 2 subfolders from the Inbox to the actual account parent (similar to trash / sent /etc folders). They continue to work properly but the inbox is still broken. I created another folder, called Inbox 2, and copied the threaded conversations from the Inbox to Inbox 2. They work perfectly. Then I copied 2 of the conversations back to the Inbox. They fail to remain threaded when leaving / returning to the folder. I don't know if I can delete the inbox and create a new "inbox".... something has been corrupted in the inbox. Suggestions ? For now, I am working out of Inbox 2 by coping all inbound mail to that folder. Thank you.