Rick I have copied Mail to the external disk. I don’t understand where or how to copy it to local folders on my macbook.

What part do you not understand?

I have the external disk with Mail and the disk is plugged into the macbook but I don’t know how to transfer this information into thunderbird local folders before copying into the server.

I wrote instructions earlier. I would rather not repeat them and add more detail without knowing exactly what part you need help with. Would you please review what I wrote earlier and let me know?

I do not understand what you mean by top level of Thunderbird and reference to library. I cannot fathom out where to look for the file you state. I have looked through everything I can. As I say the files are on the external drive. I will understand and apologise if this has gone on too long but it is not only a complicated procedure but also not smooth given the computer age.

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I do not understand what you mean by top level of Thunderbird and reference to library. I cannot fathom out where to look for the file you state. I have looked through everything I can. As I say the files are on the external drive. I will understand and apologise if this has gone on too long but it is not only a complicated procedure but also not smooth given the computer age.

Everything on a computer is stored in a hierarchy of folders. I said the top level of your user account, not the top level of Thunderbird. The top level of your user account on your MacBook is a folder named "alan" or something similar. Within that folder is a "Library" folder. Within that folder is a "Thunderbird" folder. Etc.

~/Library/Thunderbird/Profiles/[the name of your profile]/Mail/ just specifies the path from your "alan" folder to the folder in which we want to put "Local Folders".

Open the "Mail" folder on the external drive when it is attached to your MacBook. You see the "Local Folders" folder inside the "Mail" folder, right?

If you saved any new messages in local folders on your iMac since we started this project, and if the files on your external drive came from the back-up copy of your profile that we made, those new messages are not on your external drive. We would have to go back to your iMac and make a fresh copy of "Local Folders".

Let's skip the part about your user account. Instead, find your Thunderbird profile folder on your MacBook the same way that you found it on your iMac: in Thunderbird, "Help" menu > "Troubleshooting information" > find "Profile Folder" in the left column and click on "Show in Finder" next to it. You will then see the top level folder of your profile. Open it. Do you see the "Mail" folder?

Have you confirmed that there is nothing in "Local Folders" in Thunderbird on your MacBook that you want to keep?

Then close Thunderbird.

Then click and drag the "Local Folders" folder from the external drive to the "Mail" folder on your internal drive. You will have to confirm that you want to replace the existing "Local Folders" folder.

When the copying is done, open Thunderbird and confirm that all the the local folders from your iMac are there.