Describe how you went about copying the backup profile to the new PC. You must have missed or messed up a step.

Hi Stans, thanks for taking the time to respond; I appreciate it. It is very likely that I have made an error or several.

I was using a Dell laptop until three months ago when I killed it with a mug of tea. The hard drive was still OK and a friend recovered all data including Thunderbird files.

I downloaded Thunderbird App onto an iMac and simply logged in to the account I use most which is a 1&1 free account and still all working.

The second account is an email account that used to belong to a domain I owned. I allowed that site and service to lapse, and migrated all messages to a local Thunderbird folder. I have been unable to get into that account because it seems that Thunderbird seeks to verify servers for incoming and outgoing messages, whereas my data is static, just an archive.

I have the Thunderbird files from my old laptop on an external drive.

Following instructions (help docs and Youtube video) I downloaded Thunderbird, went to Troubleshooting -> open Folder. I then closed Thunderbird (without setting up any acounts) and copied the files into what I assumed was the correct place. I tried pasting "Profiles" and tried pasting also from Roaming where the "profiles' folder seems to have additional files. I have also tried these steps on a new Windows machine. The data isn't visible when I open thunderbird and I simply see the same invitation to set up accounts which fail when I cannot provide 'live' server info.

Thanks for any steer you can give me.

Thunderbird profile folders are named using a string of 8 random characters, a period, the name of the profile, and an optional suffix. For example, xpuielfk.default or tlwrcnsu.default-release. It takes the format <8 random characters>.<profile name><optional suffix>. The "default" name arises because Thunderbird creates a default profile when you launch it the first time, and it gives that profile the name "Default User". So, using the example names above, the path to the profile folders would be Thunderbird\Profiles\xpuielfk.default or Thunderbird\Profiles\tlwrcnsu.default-release. This paragraph is supposed to give you a solid idea of what a Thunderbird profile folder looks like, so that there is no confusion about what is referred to when you're told to open the profile folder and perform basic filesystem operations like opening, renaming, deleting or copy-pasting stuff in it. Details about Thunderbird profiles are available here Profiles - Where Thunderbird stores your messages and other user data

Now, assuming a complete profile folder was recovered from the disk, you can simply copy ALL its contents and paste them into the current profile folder. Let's call the recovered profile folder 12345678.default and the current one abcdefgh.default-release. The right path to the recovered profile folder will be AppData\Roaming\Thunderbird\Profiles\12345678.default and MUST NOT be confused with the AppData\Local\Thunderbird\Profiles\12345678.default path. To confirm that the recovered folder came from the right path, open it and inside you should see two subfolders named ImapMail and Mail. Those are the folders in which Tbird stores your messages. ImapMail is used for IMAP accounts while Mail is used for POP and the special Local Folders account. If you open these subfolders, you'll see mbox files (they have no file extensions) and other files like .msf files. If the recovered profile folder has these subfolders and files, then you have the right profile folder.

Go back to the root level of the recovered profile folder 12345678.default, select everything inside it and copy them. Now open the current profile folder abcdefgh.default-release, select everything inside it and delete them (Thunderbird MUST NOT be running) and paste the copied items into the now empty profile folder. Among the pasted stuff there is a file called pkcs11.txt. Delete it, then launch Thunderbird. If all goes well, Thunderbird will load that profile and everything will be exactly the way they were on the Dell.