2
Just my .02
I had the same trouble after renaming to Spanish these folders.
What I finally did (and worked), was to deactivate the module, then uninstall it.
I loaded the whole module again, overwriting everything, and installed.
My changes were in place.
To use the Sent box folder you have to config it in the preferences.
The box files folder is an archive were you store whatever message you want to.
Hope this helps you.
Warm regards from sunny México!
Pepe