SBD folders and MSF files created that shouldn't be

First this is an installation on a PC. My local folders for Thunderbird are stored on an external drive. I rarely need to go to this drive, but on occasion I store a temp file for use on another PC. I was doing just that when I noticed a large number of SBD folders and MSF files there. For general description, on that drive I have local folder for Thunderbird. I also have folders A through Z which have nothing to do with Thunderbird, just other misc. folders for temp use. Thunderbird has gone through and created a second folder for each folder A through Z and an MSF file for each folder. Each one of these SBD folders has a sub SBD folder for each file that is in the original folder and an MSF file. Is it safe to delete all of these folders since they are not any part of emails. Why and how to prevent this from happening to stop clutter in my primary folder. Thank you for any advice and help.