On the W7 computer, open the Mail subfolder of the profile folder. Use Help/Troubleshooting Information, and click Open Folder to open the profile folder, then close TB. Open the Local Folders subfolder of Mail and find the mbox files, the ones without file extensions and associated with a like-named index .msf file. Copy the mbox files into the Mail/Local Folders location on the W10 computer, while TB is closed. The folders will appear under Local Folders in TB when you restart TB.

If you want to synchronize mail over several devices, set up accounts as IMAP, which is essentially a cloud-type arrangement. Backup any mail you want to store on a local computer by copying it from the IMAP folder to Local Folders.

Synchronizing both was done correctly. However, I moved 2 messages to one of the folders under 'local folders'. They can not be found in it. Well another message that I, as far as I know, not moved ?? Also went searching if they might be under a different folder in 'local folders'. Waited until now to respond because this may only be changed once a day, but that did not help either. Moving and backing up messages to keep is not reliable?

Copy messages from an IMAP folder to Local Folders, then after you confirm the message is in Local Folders, delete the messages from the IMAP folder. When I move, instead of copy, from IMAP to Local Folders, it works properly, but in your case there may be reasons why it doesn't. It's safer to do the copy-then-delete process and avoid losing messages.

Everything succeeded: but no good result. Sorry. On the contrary: transferred a mail in the old laptop to local folders and I find it there. OK But in the new laptop I can not find that same mail anywhere! Can look it up and he will appear in the lookup list. But he can be seen in the mailing list anymore; can not be found in the local folders anymore and can't be deleted in the lookup list also!. He appears to be floating somewhere?

I have the "transfer" problem every time my Win7 computer gets hacked with a terrorist blackmail shutdown. So every night I back up the relevant TBird files to an offline storage device so that they can be restored. The *location* in Win7 is "C:\Users\rs\Application Data\Thunderbird\Profiles\GOBBLE.default\Mail" where "GOBBLE" Is the actual default folder on your computer which you can locate by stepping down through its preceeding folders in my example. When I need to restore from the offline storage device, I simply copy it over the full system restoration that I had to do (from its weekly full system backup) to regain control of my hacked physical computer.

If you move a message from an IMAP folder to Local Folders, it will be removed from the IMAP folder and stored in Local Folders on that computer. But on a second computer, the message will be gone from the IMAP folder, and not present in Local Folders on that computer. Local Folders means exactly that - mail that exists only on the local device.

A moved message may temporarily appear in the global search results of the second computer, but only until the global database is updated. It won't appear in a folder search, Ctrl+Shift+F.

The problem still remains unsolved: the local folders of the new laptop were to be placed in the cloud with the intention of creating a synchronized version in the older laptop: it did not work either. Moved mails to the local folder remain absent while, of course, those mails can no longer be seen in IMAP.

To repeat: messages in Local Folders can only be accessed by the computer on which they were stored. To make messages available to all computers with the same IMAP account, they must be copied or moved to an IMAP folder, and that folder must be subscribed on all computers that need to access that folder.