I am not clear on what is missing. The appdata\roaming directory is part of Windows, not Thunderbird, so that directory does exist. The appdata directory itself is a subdirectory of the user account directory.

AppData is hidden by default, so check 'Hidden items' on the View tab in File Explorer.

Type %appdata% in the File Explorer address box, then Enter.

David, you are correct, the appdata subdirectory is a Windows feature. But it's not there. It was there before I re-installed Windows, but after the re-install, it doesn't show up in C:\users\.

sfhowes, I don't think the appdata subdirectory is hidden. I did try to "display hidden files" in the View menu, but it doesn't work.

I conclude that I must take up the issue with Microsoft, though I haven't yet succeeded with that.

But let me ask, what is the procedure to carry all the app data from Thunderbird when you want to completely re-install windows? I don't see a way to export the data to a file that the new Thunderbird could make use of, like Chrome or Edge browsers do. I saved all the Thunderbird folder in appdata\Roaming and in a subdirectory within the Roaming subdirectory. If I paste these files into my new Windows operating system, will I duplicate Thunderbird like it was before I re-installed? Could I just create the appdata\Roaming folders under C:\Users, and do the paste and expect it to work?

Much thanks for your efforts.

The simple way to export is to use tools>export menu. That is good for profiles up to two gig.

sfhowes, I don't think the appdata subdirectory is hidden. I did try to "display hidden files" in the View menu, but it doesn't work.

https://support.captureone.com/hc/en-us/articles/360007574298-Unhiding-the-AppData-folder-on-Windows

sfhowes, thanks. Your link is for Windows 7, and I'm running Windows 10, so the info wasn't exactly applicable, but I did try some things using the "View" menu and "hidden" tabs, and now I do see the AppData subdirectory. So thanks much, because I thought that was a dead end.

David, your comments are very helpful, and I understand much more. Silly me for not looking under "Tools" for exporting and importing data. I may have screwed myself for not using this utility, but I do have (I think) the critical Thunderbird user files saved from two previous versions.

Is there a way to access this previous data without losing current data? Might there be a way to create different users that make use of my saved data? This way, I could open Thunderbird via these different users and access the data. Would this mean installing more than one Thunderbird programs, or can I use one installment with different users. Would defining different "users" in Windows 10 be the way to do this?

Is all the necessary data (inbox, address, outbox, etc.) stored in the one file in the "Roaming" directory? For instance, I have two files in the "Profiles" subdirectory: bit0jsmf.default-release and cg2yiab2.default. It seems the first file is the one Thunderbird is currently using, because I tried changing the file name while Thunderbird was running and I got a message saying I can't do that because the file is in use.

I tried the following. I closed Thunderbird and successively changed the name of the .default-release file. I then pasted into the "Profiles" subdirectory another .default-release file that I copied from a previous Thunderbird (before a computer crash). I re-started Thunderbird and got a message that the required data file "cannot be found." So I guess my question is, how do I tell Thunderbird what Profile file to use? Or, is the best way to do this by defining additional users?

I realize this is getting to the nitty gritty and it's all a result of my carelessness, but I'd appreciate any help. Basically, I'm trying to access all my data from previous Thunderbird installments, by whatever method that works. Thanks again.

Some comments: - Thunderbird does not care about the name of profiles. It uses whichever is pointed to by profiles.ini. Profiles.ini is best set by using profile manager (e.g., type 'run' at search window in windows taskbar, then enter thunderbird.exe -p to start profile manager) -extra profiles are possibly never used or incomplete. -if there are other profiles displayed, you can switch to one by clicking help>moretroubleshootinginformation, scrolling down to 'profiles' and click 'about:profiles', which will list the accessible profiles and you can select one.