The Mail/Local Folders subfolder of the old profile folder contains mbox files, which have no extension and are named after the folder that contained the messages. The default location of the profile folder is:

C:\Users\username\AppData\Roaming\Thunderbird\Profiles\8charstring.default

AppData is hidden by default.

Copy the mbox files from the old profile to the Mail/Local Folders location in the active profile, while TB is closed. When TB is restarted, you should see the folders under Local Folders in the Folder Pane. This also works for mbox files in the Mail/<popaccount> and ImapMail/<imapaccount> folders.

Hi sfhowes, Thanks so much, looks like a plan, tomorrow I will be awake enough to try it. Will get back online and confirm I hope , but certainly sounds good. Regards Princy 557

Hi sfhowes, OK lets start with a BIG THANK YOU. It works like er, perfect as you said on your tin. I've only moved about six over, but no problems with any of them.. Made a record of it for future use if it happens again. Much appreciated. Stay safe in these mad times

Regards Princy557

Just another quick question.

under the file system above I have an identical folders. On the new system there are say 5 entries from the old system I have a hundred. Is it possible to merge rather than replace this data.

Would make the process even sweeter?

Regards Princy557

To merge a backup folder with an existing one of the same name, you would have to do it manually: rename the backup mbox file to Folder2, copy it into Mail/Local Folders, restart TB, select all the messages in Folder2 (Ctrl+A), then drag and drop them onto Folder.

There is an add-on for managing duplicates:

https://addons.thunderbird.net/en-US/thunderbird/addon/remove-duplicate-messages-alte/