How to use Thunderbird to get copies on your computer so you can then choose to upload to new server or not depending upon your preferences. You basically need to get full copies downloaded to your computer and then get 'copies' of those emails into the 'Local Folders' mail account, so they are not dependent on any server. Then, if required, get copies back onto new server after swapping the server settings.

First make sure you have synchronised the relevant folder(s) for offline use in order to ensure you have downloaded full copies of emails.

• Right click on imap mail account in Folder Pane and select 'Settings'
• select 'Synchronisation & storage' for imap account
• Select 'Keep messages for this account on this computer'
• click on 'Advanced' button
• make sure all the folders you want to synchronise are selected.
• click on 'OK

• Select 'Synchronise all messages locally regardless of age'

• Menu app icon > File > Offline > Download/sync now
• Select 'Mail Mesages'
• Select 'Work offline once download and /or synchronisation is complete'
• Click on OK

Allow a little time for process to complete.

In Offline mode perform a few random checks - select emails and if you can read contents you have good copies downloaded.

At this point you have a choice. The first choice you do in Thunderbird in Offline Mode, the second choice you exit Thunderbird, access profile folders and put copies of folders in Local Folders. The latter being probably quicker if you have a lot of folders and emails. But both methods are valid.

Option 1. Stay in Offline mode as this prevents accidental synchronisation on files which you have opened and are copying loads of emails.

• Create identical folders in 'Local Folders' mail account ready to receive copied emails.
• Select batches of emails
• Right click on highlighted emails and choose 'COPY to' and select the appropriate folder in Local Folders mail account.
• Repeat until all is copied.

Please note: I say use 'COPY to' not 'Move to' because if something wrong then at least you still have the original so can repeat.

Once all is OK, I suggest you create a backup of profile folders.

Option 2:

• Menu app icon > Help > Troubleshooting information
• Under 'Application Basics' about 8th in list 'Profile Folder' - click on 'Open Folder'

A new window opens showing the contents of your profile name folder.

• Exit Thunderbird now - this is important.

You will see 'Mail' folder and 'ImapMail' folder. The 'Mail' folder will contain the 'Local Folders' folder -

• Right click on 'Mail' folder and choose to 'open in a new window'
• Select 'Local Folders' to see contents.

Leave that window open ready to receive files and perhaps move to one side.

In original profile name folder...

• Click on 'ImapMail' folder
• Click on imap mail account name folder to see contents.

You will see mbox files - they have same name as folder eg: 'Inbox', they do not have any extension and they contain emails. You will see index files that have same name eg: 'Inbox.msf' but they have the .msf extension. These index files are used by Thunderbird, they do not contain emails - do not worry about those files. You may also see folders with same name and a .sbd extension eg: 'Inbox.sbd' and those *.sbd folder mean you have subfolders and those folder may also contain mbox files.

• You need to get COPIES of all the mbox files and all the *.sbd folders and put those 'copies' into the 'Local Folders' folder.

I strongly advise you use the right click and copy, then paste into 'Local Folders' because if something goes wrong then you still have the original so can repeat the action.

Please see image below as a guide, so you can see what I mean by mbox files.

Now you will have a full copy that is independent of the server. It will be displayed in the 'Local Folders' mail account.

At this point perform a backup. Go up the directory to the 'Roaming' folder Copy the 'Thunderbird' folder to an external drive.

When you restart Thunderbird, you should see a full copy of everything in the 'Local Folders' mail account.

Once you are happy that everything is copied ok, you can then change the server settings to point to the new server as same email address will be used. Then restart Thunderbird to ensure it is set up to use new server settings. This will mean the imap account will be pointing to an empty server, so it will not display anything.

Now, you can choose to either leave all the old server emails in 'Local Folders' account where you will still have access and the imap account will only then show any new mails since moving to new server. OR you can create suitable folders in imap account and manually 'Copy' batches of emails from 'Local Folders' back to the imap folder. This is not a quick process as communication with server will be a process for uploading each email. It will also use up quota on server, which may or maynot be an issue. You may like to have a fresh clean imap account. It depends upon whether you need a copy on the server because you need access via another imap account. Basically your choice.

re :Will the folders at my new host automatically "fill" from my existing profile because it is IMAP? I hate to depend on that.

If you swap over your server settings to point to a new server, then the imap account will synchronise with new server and display what is on new server. So in effect, all folders and emails in imap account will get deleted. Imap accounts can only display what is on server.

Hence all the advise given in first comment to protect copies all your emails before you swap server settings to look a new host server.