moving the messages did not separate them from the imap account. to do that, you need to COPY to local folders and to then delete from account.

Thank you, David! Mystery solved! I appreciate your help! :) One more question: Will copying the message also make copies of the attachments? Or will attachments be gone after I delete the original messages from my inbox? Thanks!

I think all will be there. That is why I suggest a spot check after the copy so that you're content with the results.

You, you're right; I'm finding that if it copies, it's there. But I'm having a lot of trouble getting email to copy at all. I select an email holding Control (on PC WIndows 11) and drag to a Local folder, and maybe 40% of the time it copies correctly, other times it does nothing, and other times, if I try to copy a group of emails, the copies are blank. And if it does copy correctly, it takes forever. I wish I could just select a group of emails and copy them, but it doesn't work very well. I guess because it has to download everything from the account. Going forward the tools will be useful if I can keep up with it and not end up with so many large emails to copy, but right now, it's a mess.

Okay, let's regroup and start over:

1. click file>offline>download to ensure you download headers and content
2. now, install the addon, importexporttools,
3. now, highlight each desired folder, rightclick, select importexport option to export mbox and save to a windows folder somewhere
4. now, rightclick Local Folders, rightclick and select importexport option to import mbox - this should bring in everything properly
5. now, check that the messages are in the new folders and you can now delete from the account.

Thank you, David, I'll try that tomorrow. Could you please tell me if there's a way to tell if mail that's been copied to a local folder are indeed local? I'm asking because I copied more than half my emails to local folders and I've been deleting email with attachments from my inbox/sent folders in my IMAP account, however the quota meter still hasn't budged. Is there a way to find out if a message is local or linked to the account? Thanks!

There may be an answer, but I'm not aware of it. The quota meter you referenced may be something adjusted periodically, and not immediately. That is, it may be a measurement dependent on the email host's preferences, not something that is updated immediately.

Thank you so much, David, I love the add-on importexporttools! It allows me to select everything in the mail box and just let it export unattended, which is a dream come true. Plus it has the eml format option which I used to use and was disappointed when Thunderbird went to mbox, so I'm very happy to have that option again. Right now it's still saving out the files, but when it's done I'll empty my mailbox and check the quota again. I think it's like you said, the IMAP account isn't updating the quota immediately. So if it's still not updating after a while, I'll reach out to my email service provider. Thank you again, David, I very much appreciate your patience and expert help!

Thank you for your kind words. I was glad to assist.  :)