On your question about storing local folders on D drive: - exit TB - copy C:\Users\XXXXX\AppData\Roaming\Thunderbird\Profiles\23h3lpqw.default-release\Mail\Local Folders to drive D. Rename as desired. - start TB - click 'account settings and scroll down left side to 'Local Folders' - click the browse button to locate and select the drive D folder - restart TB - if all is well, the original Local Folder at Mail\Local Folders can be deleted.

I have no idea what you meant with "Local Folders - Copy.sbd" was copied" and don't know if that is relevant.

Thank you for your reply.

Folder C:\Users\XXXXX\AppData\Roaming\Thunderbird\Profiles\23h3lpqw.default-release\Mail\Local Folders is a large sized folder. Not unexpected as it should contain many email messages going back many years; I have had email addresses since the 1990s and have kept a vast number of these.

However the largest folder is "Local Folders - Copy.sbd" When I open it I see all my Local folders although if I click on the folder it shows empty. But following the folders are many files, often with an msf extension, which appears to be the actual messsages. I checked by looking at one folder then adding a new email to it; the new email now appears in the file

I will now run a backup of my D: drive with this new folder.