From the comment you provided under the other answer I assumed you have Ubuntu. Also you have mentioned that
Basically, I don't care if I use the Archive function or not. I just want to put under a different folder 2012's email, and hopefully compress and archive, too.
As I don't have Ubuntu for testing this but I got How do I back up Thunderbird emails? on Ask Ubuntu SE netwotrk and provided solution is
Go to your home folder & press ctrl +h to view hidden folders
copy & backup ".thunderbird" folder
Inside .thunderbird you should see a bunch of files and folders named
Cache, Mail, ImapMail etc
If not, then you have relocated your profile folder.
Your actual profile folder is defined in a file named 'profiles.ini'
Open it with a text viewer/editor and you will see something like
The 'Path' is the real folder to backup.