POP accounts use a 'popstate.dat' file to record what has previously been downloaded, so emails do not get downloaded again.

Obviously, something has squiffy if they are showing in the Folder Pane. Do you have anything like CCLeaner or similar that cleans up files or Anti-virus program that is allowed to scan Thunderbird profile folders ? If yes, I suggest you do not allow scanning of Thunderbid profile files and folders by any of those types of products.

In Thunderbird Help > Troubleshooting Information Under 'Application Basics' section - about 8th in list -Profile Folder - click on 'Open Folder' See image below as guide.

A new window opens showing the contents of your profile name folder.

Exit Thunderbird now - this is important

Click on 'Mail' folder to see pop mail account name folder Click on the pop mail account folder to see contents. See image below showing a typical pop account.

You should see a 'popstate.dat' file - this is normal

You may also see 'popstate-1.dat' files - delete those files You may also see the same files with a .msf extension - if you see them - delete them.

Start Thunderbird.

Thanks so much for your reply! I followed your instructions last night and no "pop-state.dat" files this morning. Thanks again!!