Hi - I transfer my updated email folders from my work computer to my home office computer every day or so, using the xcopy command to transfer all changed files in my local folders email folder and subfolders to a USB memory stick that I use for keeping my data files synced across the two computers. I noticed a couple of months ago that after doing my update for Thunderbird on (say) my home office computer, that when I then retrieve email in Thunderbird from my (main) AT&T/Yahoo account, ALL email over the past few days is downloaded, since the last time I updated on my home computer. In other words, even though I have already retrieved dozens of emails into Thunderbird using it on my work computer, the same files are downloaded from my Yahoo inbox again (those that are still in the online inbox). This is a hassle. I believe that there is some Thunderbird .js or .json file that keeps track of the email that has been downloaded, but it is not getting copied when I do my backup from my (say) work computer to my USB stick that I use for transporting the files to my home computer. If that is correct, what file or files am I missing, that I should be copying to the USB stick so that only new email are downloaded to my home office computer when I next use Thunderbird at home (after, of course, running my update batch file to copy the new files to my home computer)? Thanks! Bruce