Maybe Thunderbird opens 8 times, causing it to use very much memory, constant swapping and not being able to receive mail. Thunderbird remembers the session settings, so it will always try to restore all windows after a restart.

Try closing the excess windows, or open Windows Explorer and go to your profile folder to remove or rename the file called session.json, which holds the information about the opened windows.

You can do this by opening Windows Explorer and type %APPDATA%\Thunderbird\Profiles in the location bar. Then double click on your profile folder and search for the file called session.json and delete or rename it. This should be done when Thunderbird is not running, or else Thunderbird will overwrite the file again upon exiting.

Thank you so much, this problem has been so irksome for a long time. After I found out from Wikipedia that Windows Explorer is now known as File Explorer. I was able to follow your advice in your 3rd paragraph. It worked, can't thank you enough. All good wishes to you.

I'm glad it helped. My father had the same problem and when checking it appeared that Thunderbird opened 59 times! In order to prevent the problem from reoccurring I made the file session.json read-only on his system, so that session history isn't saved anymore.