There may be an error in your profile. That can happen if Thunderbird crashes or if the profile is copied while Thunderbird is running. Another way to import thunderbird is by clicking Tools>import and selecting the option to move from another machine. Select the desired profile and see if that works. Otherwise, I think there is a profile problem.

As I said in my original post, I tried the Import tool as well. What seemed strange is that when I downloaded a fresh copy of Thunderbird software onto the new machine, and then tried to open it so that I could start the transfer process, I got the "Profile Missing" message (i.e., before I tried to migrate the old profile on Windows 10 machine to the new Windows 11 machine). In other words, it wouldn't let me open/use what should be a virgin copy of the software.

I am still not successful in migrating Thunderbird from Windows 10 to Windows 11 machine. This time, I made sure that all Thunderbird files were deleted from new machine [discovered that Uninstall does NOT remove all data files]. Followed instructions for copying and pasting Profile, etc. Downloaded a fresh copy of Thunderbird.

When I open the new Thunderbird, it acts like I didn't upload my old Profile -- but when I open Profile folder, all the transferred files are there. Why doesn't it recognize all my old data, accounts, etc.?

Sequence of events may be important. Install TB first, as it creates dummy profile. If yours was loaded first, it won't see it. If you're copying from old ....\appdata\thunerbird that should work. If you're copying from old ...\appdata\roaming\thunderbird\profiles then you may need to set profile manually. When opening profile afterwards, be sure to view in Thunderbird at help>moretroubleshootinginformation and scroll down to click to 'profile folder' and click 'open folder' - that ensures you're viewing the folder in use.

Hi David, thanks for your help. I truly believe I followed every step in the instructions on the Support page. I did download the fresh copy of Thunderbird onto the new machine before copying and pasting the profile from the old computer. Here's what I have: 1. The fresh copy of TB did create what you called a dummy profile. It was named kixomwm3.default-release

2. When I open the new TB and go to the troubleshooting info page, and choose Profile Folder, it opens to that same folder, namely, Thunderbird > Profiles> kixomwm3.default-release>, and in fact, I can see all the data from my old machine in that subfolder.

3. When I go to the troubleshooting info page and click on About Profiles (near the bottom of the list) it lists 2 profiles. The first is Profile: default-release It says Default profile=yes, and lists the root and local directories as kixomwm3.default-release. The second is "Profile: default". It says Default profile=no and lists the root and local directories as a different folder that is almost empty (it only contains 2 files: parent.lock and times.json)

In summary, everything seems to look as I would expect it to. The only thing wrong is that when I open TB, it goes to the pages you get when starting to use TB for the first time; that is, 2 tabs: Account Setup, and Home "Welcome to Mozilla Thunderbird--Choose what to set up"

I am so frustrated! What am I doing wrong??

I am having similar problem. My PC got messed up when I inadverdently cut power to the PC while it was shutting down. Programs could no longer find their data files. So, I decided only recourse was to do a W10 reset. Before resetting, I copied my Thunderbird Profile to a USB drive just in case. After reset Thunderbird works but doesn't find any of my past data (contacts, emails). So i copied my Profile files off of the USB to the PC.

I did not use the Export function to copy the original Profile to the USB drive, just used File Explorer to copy and past. It is also likely that Thunderbird was still open when I did the copy to USB drive. Is my historical data gone if Thunderbird was still open?

John

Also, my original Profile I copied was in file location ....\Mozilla\Firefox\Profiles\

After resetting W10 and reinstalling Thunderbird the path is now ...\Roaming\Thunderbird\Profiles

Did I copy my original Profile from the wrong location?

John

@mike - if Thunderbird keeps starting that way, it means the default profile has an error or has no account defined.

@john, the profile for thunderbird is always at ...\appdata\roaming\thunderbird and yes, if profile copied while Thunderbird is running, some folders or files are not copied because they are still under Thunderbird control.

So what are my next steps? I have been using TB for years, and do not want to lose all those years of history, contacts, etc. by starting fresh. What do you suggest I try?

Do you still have old PC? If so, will thunderbird start there ok? If so, what version is it? That may be a clue.

If that isn't possible, it may be time to create a fresh profile. In your copied profile, you have your addressbook (abook.sqlite) and your message folders. If IMAP, they will be recreated automatically. If POP, I suggest creating the account, but omit password to ensure it doesn't attempt to download messages yet. Then, with Thunderbird not running, copy all content from the ....Mail\account\ folder to the corresponding Mail\account\folder, overlaying the default content. The addressbook can be copied to the profile, replacing the default. If there were folders in Mail\Local folders folder, copy those as well. Now restart thunderbird and check that all is okay.