re ;I had downloaded email folders from a webmail acct. This means you had correctly created an IMAP mail account in oder to remotely connect to server folders. You subscribe to see folders and then choose to synchronize if you want to get a copy of folders on your computer so that you can work offline.

re: I was adjusting the address for Thunderbird to obtain emails

When you created the account I presume the email address was correct because you were already able to see the remote folders.

So why would you 'adjust the email address'? This is illogical and makes no sense at all. When you altered the email address you were no longer looking at the correct server, so you would not see emails.

If you have two email addresses then you would need to create another mail account for the other email address.

suggest you fix the mail account to use the correct settings and then you can connect to the correct server.

Let me give you the long story. I am moving my website from one registrar to another. Before moving, I installed Thunderbird so that I could download my web-emails before they disappeared. All the folders were downloaded into Thunderbird. Then I pointed Thunderbird to my new web-mail address for my new location for my website. Somehow, in setting up Thunderbird, the folders disappeared. Luckily, the web-emails were still on my old website location. (It seems the website location change doesn't become final for 3-5 days). I downloaded them again. I immediately did a partition backup.

Since the Folders are not on my new web-mail server, I am concerned about the correct Thunderbird synchronization settings. What setting do I need to keep the Folders that I have on Thunderbird (not from my new webmail location) and still see all the web-emails on my new webmail location?

Does Thunderbird have an internal backup capability? Or what file names hold all the email and folder data? Can I copy/backup just those?

old website server - Connect to server by resetting the account details to the correct orginal settings and subscribe to see folders. Then synchronize all folders, so you keep a copy on the computer. 'Keep messages for this account on this computer' should be checked if you want to synchronize messages between your local system and your mail server. see: https://support.mozilla.org/en-US/kb/imap-synchronization#w_configuring-synchronization-and-disk-space-usage

When all folders have been synchronized you will have a copy of all emails and folders on your computer in your profile., but they can still be altered if they resynch with server. So, go into 'offline' mode, which will stop any connecting with server.

In offline mode (two black screen icon shows in bottom left of Status bar), move all folders with emails into Local Folders. Local folders is a special default account in your profile folder. The folders and emails in Local Folders are on your computer and will no longer be connecting to the server.

Do not change/modify the old imap account settings. When you are certain that all emails are in Local Folders, remove/delete the mail account. Tools > Account Settings select the old imap mail account name click on 'Account actions' select : Remove account' click on OK

Create a new imap mail account for the new server settings. As folders are viewed remotely, these emails are on the server, so when you create a new imap mail account to connect to that server, you will see all your subscribed folders and their emails.

You can continue to see old emails in Local folders. New Imap mail account will show the new emails in that mail account.

I have 3 folders under ARCHIVES. All 3 folders & contents are on my laptop. I tried to drag & drop the folders to LOCAL FOLDERS while OFFLINE. The folder titles were moved but had no content. The 3 folders with their contents remained under ARCHIVES. I tried to delete the empty folders under LOCAL FOLDERS, but it wouldn't let me. The IMAP settings are pointing to the new server. What next?

I have 3 folders under ARCHIVES. All 3 folders & contents are on my laptop.

Can you clarify exactly where the Archive folder is on the laptop? I'm trying to understand how / what format they are currently saved.

Is the Archive folder currently viewable in Thunderbird on your Laptop? so that it is a Thunderbird Profile folder on your laptop. If yes, is it in Local Folders or an IMAP Archive folder or a Pop mail account?

If the Archive folder not in Thunderbird, but say on your laptop desktop, is it a windows folder you created? When you open Archives folder do you see the three folders or files.? do you see mbox files that have same names as your folders with their same name .msf files ?

or do you see 3 folders and the contents are .eml files?

Please provide image of the contents of one of the folders?