I followed the instructions for transferring Thunderbird data from an old PC to a new one. ("Moving Thunderbird Data to a new Computer"). The only email messages that made the transfer were the ones I saved from Outlook Express that were imported into Thunderbird on the old PC in 2014. None of the emails existing in my two important account folders (set up in 2014) made the move. Those, of course, are the most important ones. Now what? PS: I am not an IT professional, just a small business owner that needs to transfer emails from the last couple of years to a new PC because the old one is obsolete. PPS: It was not possible to install Thunderbird on the new PC without creating an account - - the installation program refused to move forward to complete the installation without doing this step. If I understand the instructions in "Moving Thunderbird Data to a New Computer, I was not supposed to create any accounts during the installation process. However, that proved impossible - - the installer would not complete the process without doing this and there was no option to skip creating accounts. After I made my first attempt to install the "Thunderbird" folder (containing the Profile folder, etc.) on the new PC, and finding my most important email messages didn't make the trip with the rest of the Thunderbird folder, I tried deleting the account I had set up as a required step in the installation process in order to install TB on the new PC, then uninstalling Thunderbird, in order to clear the account that I had set up (one of the ones I am trying to transfer over). In other words, I tried to start over with installing Thunderbird on the new PC. However, when I downloaded and installed Thunderbird the second time on the new PC, it reinstalled the account I had deleted!