IMAP syncs the local mail client with the mail server, which it appears you have now. POP downloads the Inbox only, and if messages are kept on the server after download, a deletion in TB is not mirrored on the server. But if you copy messages from an IMAP server to Local Folders, those messages are retained no matter what is retained on the IMAP server.

To change an account from IMAP to POP, the account must be added again as POP:

http://kb.mozillazine.org/Convert_a_POP_account_to_a_IMAP_account

Thank you very much. You said, "But if you copy messages from an IMAP server to Local Folders, those messages are retained no matter what is retained on the IMAP server." However, when we have deleted items from the server, we are seeing them disappear in Thunderbird as well. Are you saying that there is an additional backup copy stored on our computer that reflects downloads, not the current state of the server? If so, how would we access it and the emails if needed.

Also, if we switch to POP, I'm assuming that all of the emails (and there are a lot) will have to be downloaded again. Is that correct? Thanks.

Are they disappearing from TB's Local Folders when you delete from the server, or disappearing from TB's subscribed folder? The latter makes sense with IMAP. To be absolutely safe, mail can be saved outside of TB by Save or Export commands, and imported when needed.

If you change to POP, TB will automatically download what is on the server, but you can choose to download headers only, or move older mail to another folder through webmail before the change, as POP downloads just the Inbox.

There is something called Local Folders in TB that sits underneath the Inbox and subfolders created to mirror the server. However, all that is showing under Local Folders is "Trash" and "Outbox". I dug around in the Account Settings and found a link to a Local Folders folder stored on my computer, but nothing is in it. It is empty. I also set the Message Archives to store in this Local Folders directory, but still nothing is there.

Regarding Save and Export, I don't see these options. There is an Import option under Tools, but no option to Export. I see a Save As option, but that only appears to save a template, not the emails that have been downloaded.

Just when I think I'm getting close to getting this figured out, it seems to go the other direction. If I were to find a way to Save or Export what has been downloaded, could that file be Imported to the new POP account if I create one? Also, that link you provided is for going the other way, from POP to IMAP. I'm needing to do the opposite, right?

Create a subfolder of Local Folders and copy or move messages from IMAP folders to the subfolder.

The Archive folder is created when you archive the first message (press 'A').

Save messages to eml files with Ctrl+S. Other options are available with ImportExportTools NG.

There's no need to move mail from Local Folders to POP account folders, since both store mail on the local computer.

To change from IMAP to POP, copy mail from the IMAP folders to Local Folders, remove the IMAP account through Account Actions in Account Settings, then add the account as a POP account.

Okay, I think I'm starting to get it. Thank you for your patience. So I can essentially create a folder structure under Local Folders that replicates what is above under the main server Inbox, but these emails will not be affected in any way by server activity, right? Then, I won't have to worry about the POP option because we will have the backup we need of these emails.

If I am right, then that only brings up 2 more, and much smaller, questions:

1) I have tens of thousands of emails in the server Inbox. Is there a fast way to copy and paste 60,000 emails to the Inbox folder created in Local Folders?

2) Is there a way to have every email that comes into the server Inbox also copy to the Local Folders Inbox so I don't have to copy them all manually?

To convince yourself, copy a message to Local Folders then delete from the IMAP folder, and see if the copy is still there.

Select the messages (Ctrl+A to select all), then right-click, Copy to, choose the target folder.

Create a filter that copies new mail to Local Folders.

Okay, things are looking much better now. I have the Local Folders set up and have copied all of the emails from the server side to the Local Folders side. Only problem I'm having now is the filters. I've used similar filters in Outlook before, so I understand how they work. But the TB one that I created to copy items hitting the Inbox on the server to the matching folder in Local Folders is acting really really buggy. If I manually try to run it, it locks up with the activity wheel spinning forever. Then, it creates duplicate older emails in the target folder but never seems to get the new ones moving the right direction. It is really strange. It's frustrating, but I'm okay. I can just manually move each day's emails over every morning if I have to. I'd rather do that than have it creating a bunch of duplicates that take up space.

Thanks for all your help and patience. I really appreciate it!!!

I've attached a picture of a filter that should work for copying to Local Folders. Enable the filter log to possibly see why yours isn't working.

Hmmm. I was using "Match all messages". Do you think that was the problem and why it was creating duplicates? I will try this filter today once I get caught up and I'll let you know how it goes. Thanks again.

'Match all messages' doesn't apply any rules - the filter is applied to all messages every time there's a check for new mail, so it will copy any message in Inbox. It's usually invoked for one-time application of a rule or manually-run only.