I've been keeping my old mail since 2003. It's kind of my second brain, useful for referring back to transactions or agreements I've mostly forgotten. There's quite a lot of it, and I don't want to clog up my server with it, so I periodically drag emails from my IMAP Inbox, Sent, and Trash to folders in Local Folders. I started this process years ago before Thunderbird began automatically making an "Archive" folder for each account. Coincidentally, when I began archiving my old mail this way, I put it in a folder in Local Folders named "Archives". My Archives folder has yearly subfolders ("2003 Mail", "2004 Mail", etc.) and subfolders within those for "Sent" and "Received". Of course, I also have an Archive (without an s) folder in my IMAP account and in Local Folders, but the Archive folders are empty. I keep my email folders (the Local Folders "Local Directory") backed up using Google Drive for Desktop. This system worked well for years, and I've managed to use this system to move mail from computer to computer. Lately, over the past two years, I've noticed that large chunks of email that I recently moved from my IMAP account to Local Folders have disappeared. The first time I noticed it I attributed it to some kind of random glitch, perhaps my own mistake somehow. Since then, I've watched the process more carefully. I'll move a chunk of email, watch for it to finish, and then check the Archives subfolders to see that the number of messages increased by the number of messages I moved. Everything appears to be there, but then a few weeks later when I'm trying to dredge up some old email, I find that the entire chunk of email that I moved is no longer in my Archives subfolder. This last time, I lost all of my Sent and Received emails from April to June. In effect, instead of archiving three months of email, they somehow got deleted, even though they were definitely there a few minutes after moving them. I've seen recommendations that we should never move more than 1,000 emails at a time. I'm generally moving fewer than that, maybe 300 or 500 emails, two or three months' worth at a time. I know that moving my emails off IMAP means they reside without backup on my hard drive, which is why I began backing them up with Google Drive. Of course, at this point Google Drive has backed up the much-reduced version of the files that contain my emails, so they're just gone. Has anyone ever heard of losing emails like this? Even though this worked great for at least 15 years, maybe I'm somehow doing something wrong now?