If you need to convert a stack of Outlook MSG files to MBOX format for use in Thunderbird, I’d strongly suggest giving the BetaVare Export MSG to MBOX a try. I used it during a recent project to migrate a large batch of MSG files, and it handled the task effortlessly. The software is user-friendly you can add individual files or entire folders, select MBOX as the target format, and the conversion is done in no time. It preserves all email details like attachments, To, CC, Subject lines, and even keeps your original folder hierarchy intact, which really helps with organization. It works seamlessly on all windows and outlook versions. If you're looking for a simple, reliable, and efficient way to make the switch to MBOX, this converter won’t disappoint.