I have never had to do this, so the following is just my best guess.

Take your computer offline. Restore your backup (you only need Roaming) and start Thunderbird, and change your settings.

Then re-connect to the 'net.

Hi Zenos, I kinda tried that, but without the disconnect from the internet part. The reason being that I'm doing this for a non-computer-savvy relative and therefore I need to maintain TeamViewer connection. I did, however, put TB off-line as soon as it started, checked that all the Retention tabs were set to "Use my Account Settings". But when TB did go on-line I'm guessing the fact that the emails were now missing from the gmail end it started to resync and delete them on TB as well.

I restored the Local folder backup so that the Retention Policy would be set to default but that didn't seem to happen. There are no other places for TB setting are there?

Steve

ok, it is a trick or treat. "This is messy"

This can be done simply using the file system, but in the interests of keeping it as simple as possible.

Install the import export tools add-on. https://addons.mozilla.org/en-US/thunderbird/addon/importexporttools/

Now create a folder in Local folders and select it. Right click Select importExportTools >import mbox file In the dialog Select the last option with "also in sub directories" and open file picker Point the file picker to the backup (I am assuming the files as just normal files and not in an archive of some sort. IF the backup is in some sort of archive format you will have to restore the relevant files into another location to import them.) let the import go and continue on any timed our scripts. The tool does get bogged down on very large imports sometimes.

Once the mail is imported to local folders, individual mails or groups of mail can be dragged into the IMAP folders. Folders can not be dragged and dropped, only emails.

Note here that at the file level a folder is represented by an MBOX file with the same name. So the Thunderbird inbox folder will appear on disk as inbox. It will normally have an MSF file with it. This MSF file can be deleted and will be regenerated, but it makes locating the relevant files easier to look for pairs. Sub folder of say inbox will be in a disk folder inbox.sbd

Hi Matt, Thanks for the detailed "simple" solution. I'll try it out with my relative on Monday. Looking at my own TB install, in addition to the INBOX, INBOX.msf files and INBOX.sbd folder I also have an INBOX.mozmsgs folder that contains many .wdseml files. Are these important/imported? Or are they wrappers for the actual emails. Thanks for the help. Steve

I did say it was messy. For those that are happy with the file system you can just copy the MBOX files to local folders with a new name and start Thunderbird, as the format is native Thunderbird will see the file and generate indexes. But while simple, most folk do not cope with the file system.

My personal opinion is the whole mozmsgs thing is a waste of disk space.

When you first get Thunderbird you are asked if you want windows search to search email. A silly question to ask a new user. Of course they want it. They have no idea what it means or what it does, so they play safe and nswwr yes. I did the same thing myself. If you click yes, the mozmsg structure and files are created and all mail is duplicated.

The wdseml files are a standard EML mail file (text) with the attachments stripped out. Their sole purpose is for windows search. Thunderbird uses them not at all.

So unless you actually use windows search to search your emails (and I would wonder why as Thunderbird has three search options of it's own) simply turning off the windows search option and deleting the files can return many gigabytes of disk space. I think I got back about 5Gb when I finally killed windows search. I would assume not creating and updating those files would make Thunderbird faster as well. But that is just an assumption.

The option to change the setting is on the toolbar > Options > Advanced >General

Matt, Much appreciated!! Happy with the file systems. At the least that gives me a second option. I've always used the TB search - much easier than the Windows one. My relative was getting "Not Responding" messages in TB, maybe switching off the search would help. Steve

Not responding is a very wide topic.

it can be caused by windows... I though my issues were Mozilla products, until I finally noticed it was other applications as well, just I spent most of my computing time in Mozilla products. So if it is Windows 10 perticularly look to the windows 10 freezing tutorials. There are lots and lots of them.

You might also have a look here https://wiki.mozilla.org/Thunderbird:Testing:Memory_Usage_Problems WHile the wiki is about memory, the investigative staps are really the same for not responding. Not the least of which is Thunderbird own safe mode.

Finally the choice of anti virus is also relevant. We have some information on those here https://wiki.mozilla.org/Thunderbird:Testing:Antivirus_Related_Performance_Issues