Migrating programs from one macbook to another, Thunderbird failed to migrate.

I have no idea what Apple's idea of "migrating" Thunderbird would be - that would be a question to ask of Apple and would be beyond the scope of this forum. My advice may be of limited value, but it should be fairly easy to do manually if you still have access to the data on the old computer. What you will need is the folder called your "Profile", which contains all your email and preferences, and is separate from the program itself.

- On the old computer, start Thunderbird and click on <Help | Troubleshooting Information>. Scroll down to Profile Folder, then click the "Open Folder" button. Close down Thunderbird.

- Go up a level, maybe two, until you're in a folder that contains a file named "PROFILES.INI". Close Thunderbird. Copy this folder to a convenient temporary location on the new computer, using a thumb drive or other method.

- Install Thunderbird on the new computer. Start it up, and if if starts to prompt you to set up an account, decline, and quit Thunderbird.

Copy (not move) the profiles folder from your temporary location to the equivalent location on the new computer, overwriting its contents. If my directions were good and you were able to follow them, when you next start Thunderbird on the new computer, things should work pretty much the way they did before. You might have to re-enter your credentials for some accounts.

When you're satisfied that things are working as expected, you can delete the temporary Profile copy.

I have no idea what Apple's idea of "migrating" Thunderbird would be - that would be a question to ask of Apple and would be beyond the scope of this forum.

macOS has a function (facility) to transfer all data from one Apple computer to another Apple computer with the "Migration Assistant" https://support.apple.com/en-us/102613 So in John's case normally the Thunderbird app and the Thunderbird profile should have been transferred to the new Mac.

Sounds like I will need to follow Lin's direction and move the program from the old to the new computer. Thanks!

Perhaps more simple:

1. Install Thunderbird after downloading it from https://www.thunderbird.net/en-US/thunderbird/all/.
2. Check to see if Migration Assistant copied the folder ~/Library/Thunderbird from your old computer to your new computer. If it did, everything should work. If it did not, copy the folder ~/Library/Thunderbird from your old computer to your library on the new computer.