OE Mail uses a standard database technique. Each "folder" actually consists of two files. The *.MBX file is the main data store. All your messages are in there, along with other information, encoded in binary characters. The other file is an *.IDX file, which is an index to the *.MBX file. OE reads the *.IDX files to learn how to display the stuff in the MBX file.
It isnt associated with anything (It isn't there). Anyway guys, thanks for ur help, I have moved them and restarted the system and all seems to be fine. I will run the system for 2 weeks to see if there are any ill effects then I will delete them