Where Are Email Folders?

I'm a long time user of SeaMonkey and have recently started to have problems with sent messages not being copied to the selected Sent folder.

I recently set up Thunderbird Portable and attempted to import the emails from my SM folder, but totally impossible to do, from what I see. My SM folder has a separate folder named Mail, but I cannot find one in my Thunderbird folder. I figured I could copy the appropriate folders and files and it would probably work, but I can't find them to even attempt this.

Anyone know where they are or how to do the copying? I'm using the most recent versions of both SeaMonkey portable and Thunderbird portable, on Windows 7.

Thanks for any help.

P.S. Please remove this captcha nonsense.