I'm not quite sure how you've set this up.

When I installed TB, I went through all the settings and programmed it to download emails and to delete them off the server immediately.

I then move emails into the offline section of the program when I want to save them, having made personalised folders.

That is exactly the setting that I'm looking for. In past versions I had it set up to do exactly that. However, the version I am running now does not appear to give me that option. I've looked EVERYWHERE and cannot find it. I was hoping that someone could point it to me, that way I am not at the mercy of the server regarding my emails.

Set the account up as POP and it will download to PC and delete from server.

David, thanks so much for the reply. How do I do that? I don't see any place to make that change. Under server settings it does say "imap mail server" but I don't see any place where I can switch it to POP.

That's correct; you cannot convert IMAP to POP or POP to IMAP. Instead, you must create a new account. If the IMAP account is no longer needed, you can delete it.

OK, you lost me here. Forgive me, I'm going to (somewhat purposely) be obtuse. How do I do that? How do I have two accounts in the same program with the same email address? And then how do I import all my old messages to the new account?

For that matter, I don't even see a place where it allows me to create a new account.

just set it up. thunderbird can handle the same email address in multiple accounts. The POP account will automatically download all messages on the account. There is no need to import anything. If it's easier to understand, just delete the IMAP account first.

to create an account, click the hamburger menu and click 'create account. Or, with the menu bar, click File>new>email account