Work through the following to make sure a full backup of everything.

1. Check you have a full download of everything in Thunderbird.

• 'Account Settings' > 'Synchronisation & Storage' for imap account
• Check the following is selected
• Select: 'Keep messages in all folders for this account on this computer'
• Click on 'Advanced' button
• Make sure all folders including subfolders are all selected.
• click on 'OK'

Under 'Disk Space' section

• select 'Synchronise all messages locally regardless of age'

Do the above for all imap accounts.

2. Suggest you Empty the Spam and the Delete folders so not backing up stuff you do not want.

3. Run a compact on all folders to remove any old previous deleted or moved messages from files, so they are clean and tidy. You can do a compact per account:

• In Folder Pane
• Right click on name of account folder and select 'Compact'
• Details of compacting appear in the bottom Task Bar

4. Force a check to download and be up to date. Make sure the 'Menu Bar' toolbar is displaying - the one that has 'File', 'Edit', 'View', 'Go' etc If not displaying:

• 'Menu app icon' > 'View' > 'Toolbars'
• select 'Menu Bar'

Using 'Menu Bar' toolbar:

• 'File' > 'Offline' > 'Download/Sync now'
• select 'Mail messages'
• At this point - if desired - you can double check all folders are selected by clicking on 'Select' and then click on 'OK'
• Click on 'OK'

Wait a few moments for Thunderbird to make sure everything is up to date.

5. Exit Thunderbird now

6. Perform the backup: Access the 'Thunderbird' folder that contains all profile data including Mail, Accounts, Address Books, Calendar, etc etc. If using Windows OS and you originally downloaded Thunderbird from the official website: https://www.thunderbird.net/en-US/thunderbird/all/ Then profile by default will be here - (please let me know if you Thunderbird from another location eg: Windows App Store as the profile will be a different location.)

• In Windows search type: %Appdata% - see image below as a guide
• Select %Appdata% file folder
• Select 'Roaming'
• Copy the 'Thunderbird' folder
• Paste that 'Thunderbird' folder into an external disk drive

You can start Thunderbird and use as normal.

If using Linux OS then same process as the above until 6 The profile location depends upon what you used to install Thunderbird Did you use 'Snap' or 'Flatpak' or get install from the official Thunderbird download website ?

Super. Big thank you. Thunderbird was part of the original programs that came w my (plain) Ubuntu 24.4 LTS.

re: Ubuntu 24.4 LTS. I believe that comes with thunderbird installed as a snap app.

For anyone reading this who uses a Linux OS, the location of the .thunderbird folder containing everything to do with profile data may depend upon where you got the installation, so I'm offering various data storage locations to check out.

Linux OS: You need to copy the .thunderbird folder to get copies of all profiles, mail accounts, emails, filters, address books, calenda data, preferences etc etc.

Linux and Unix Profile folders are usually located here and if installed using download from official webpage then this is the default location used:

• ~/.thunderbird/<Profile name>/

The tilde character (~) refers to the current user's Home folder.

However, if you're using a third party build from Debian or Ubuntu, those builds might store your profile folder here and call it .mozilla-thunderbird - not sure if that has been altered in recent years to be same as the one above, but I'm adding it just in case.

• ~/.mozilla-thunderbird/<Profile name>

For anyone who installed using snap, the .thunderbird profle folder may be here:

• ~/snap/thunderbird/common/.thunderbird

OR in the default location if you already had a profile running before choosing to use an install using snap

If installed using flatpak, the profile directory, is usually located here: $HOME/.var/app/org.mozilla.Thunderbird/cache/.thunderbird