The folders in OE are really files with the emails compressed. For each OE folder there is a file of the same name with the extension dbx. There is also a file called folders.dbx which OE needs to decode the compressed files.
A very useful little program is available for free download called DBXtract click here (there is also a newer version for only $7 click here). I only have experience of the free version. This program extracts all the emails in a folder (file) as eml files which can be read by OE. The eml file is a text version of the email.