After a lot of effort trying to figure out how to get some of my email into Thunderbird, from simple email files, I finally figured it out. I couldn't do some of the other suggestions, as I have a lot of mail. Hopefully this saves you some pain too.
You'll need to install these tools under Linux. For Debian variants, that's the following two packages.
Follow these steps, and you should have your mail in Thunderbird's local folders.
- mu mkdir maildir
- find Inbox* -name '*.eml' | while read -r mail; do echo "$mail"; cat "$mail" | getmail_maildir ./maildir/ ; done
- Make a maildir folder in your thunderbird Local Folders.
- rsync -av maildir/new/ ~/.thunderbird/xen72crz.maildir/Mail/Local\ Folders/Inbox/cur/
- Right click folder in Thundebird -> Properties -> Repair Folder
Keep in mind that the '/new/' on the #4 line may be '/cur/'; I've seen it be either, not sure why.