You need to track your profile folder down, but be careful, there's more than one.
Take a look at some thing like:
C:\Windows\Profiles\[your name]\Application Data\Thunderbird\Profiles\default.***\Mail
and save the Mail folder.
You will be able to see by the size of the folder and its contents if you have it right.
Your path many vary slightly, but if you use the Search facility in Windows Explorer, it should give you a good idea where to look.