Suggestion: If this is a POP mail account. Tools > Account Settings > Server Settings for the pop mail account Uncheck: 'check for new messages at startup' uncheck: Check for new messages every xx minutes' uncheck 'Automatically download new messages' click on OK

If IMAP mail account......and you had previously been synchronising your subscribed folders to get a copy in thunderbird.

Go into 'offline' mode. click on two blue screen icon located bottom left in Status Bar

Create suitable folders in 'Local folders' account. select a folder to see emails. highlight emails. right click on highlighted emails and use 'Copy to' and select desired folder in Local Folders.

check emails have been copied over correctly; select an email and read it. Once emails are copied over ok, you can delete the emails in the imap folders and then remove the account. Tools > Account Settings select the imap gmail account click on 'Account Actions' select 'Remove account' click on OK

Go into 'online' mode. click on two black screen icon located bottom left in Status Bar

All emails will be visible in Local Folders account.

It is indeed set up as an IMAP account. Under 'Synchronization & Storage' I have always had it setup with "Keep messages for this account on this computer" checked though, so the messages should be downloaded already, however when I try to move them into the new folder under 'Local Folders' while in offline mode I get the error:

"While working offline, you cannot move or copy messages that were not downloaded for offline use. From the Mail window, open the File menu, choose Offline, then uncheck Work Offline, and then try again."

When downloading messages for offline use, it tried to connect to the server, which it can't do because the account is deactivated. The email should be on my system, though, because it has been setup to do so as I mentioned above.

When not in offline mode, I get an error that the folder is full despite the fact that's a brand new folder and is completely empty.

try this manual move:

Make hidden files and folders visible:

• http://kb.mozillazine.org/Show_hidden_files_and_folders

In Thunderbird

• Help > Troubleshooting Information
• click on 'show folder' button

a new window opens showing the contents of your Profile Folder Name folder.

• Close Thunderbird now - this is important.

you will see a 'Mail' folder - this folder contains the 'Local Folders' mail account, where you will need to copy paste files into.

• Click on 'ImapMail' folder

you will see the imap mail account name(s).

Make a temporary backup of the gmail imap mail account name

• Right click on gmail mail account name and select copy.
• Paste it onto the desktop for now.

• Back in the 'ImapMail' folder, click on the gmail mail account name.

You will see a list of 'Files' that have the same name as the folders that display in the Folder Pane. These are the mbox files that contain emails. You can check to see if emails are in the mbox file - mbox files can be opened using 'Notepad'. Emails are listed one after the other. You should also see same name files with a .msf extension. These are indexing files - no emails.

If you have sub folders in the folder pane then you will also see folders with a .sbd extension. These will also contain mbox files and their .msf indexing files.

For now, I would not worry about creating subfolders. It is more important to get those emails into Local Folders. You can move things around, if required, later via the Folder Pane.

• Rename 'Inbox' File to 'OldInbox'
• rename 'Inbox.msf' to 'OldInbox.msf'

• Right click on 'OldInbox' File and select 'Copy'.
• Paste that file into the 'Local Folders' mail account.

Local Folders mail account is located in the 'Mail' folder as previously mentioned.

• You need to locate all your mbox Files and their .msf files and copy paste those files into the 'Local Folders' mail account.

• Restart Thunderbird.

At this point, you should still see emails inthe 'gmail' account, but you should also see a list of folders in the 'Local Folders' account. Check you can select folders and read emails in the 'Local Folders' account.

When you are happy that all emails are now displaying in the Local Folders mail account, you can delete the emails in the imap gmail mail account. then right click on those folders and select compact. This will completely empty those imap folders. Right click on 'Deleted' folder and select 'Empty Deleted'.

Then remove the gmail imap mail account via Account Settings.

Now create a backup of the Profile Folder Name folder which is probably called 'xxxxxxx.default', where the x's are letters and numbers. Remember to close thunderbird first.

If all emails are showing correctly in Local Folders and you have created a backup of the entire Profile Folder Name folder, then the temporary backup on the desktop can either be deleted or you can save it to an external device as it does at least have copies of emails. Just in case - but those copies should also be int Profile fodler name backup.

If you are unsure about which files to copy paste, post an image showing the files in your profile imap gmail account and I'll confirm.