Given the dearth of responses you have received, I do not think I am alone in having no idea what your tool is or what problem you are trying to recover from is. But I can say your not going to find some magical method to merge the contents of mbox files.

So what is the problem rather than the solution that has not worked for you.

WOW given your sarcastic and patronising response I think I will try and work it out myself

Thanks a lot "Top 10 Contributor" and Moderator to boot

Fine, you ask a nonsensical question, trying to fix something that can not be automatically fixed and being told so is apparently "patronising"

You have the bull by the horns and are most unlikely to get to a resolution you want. But of course me telling you this is patronizing and sarcastic. If you want assistance with this tool bitrecover-mbox-fixer I strongly suggest you ask the author. No one here has apparently ever heard of it or used it, or they would have been falling over themselves with advice.

Using google I learned the product was designed with converting mac mail mbox files in mind, but the format they use and Thunderbird have not been the same for around a decade. So it would be very much a "your mileage may vary" choice to start with. It might work for what you wanted or not.

What I do know is an mbox file is a family of file formats and really I have no idea which that tool might have chosen to use or if Thunderbird can even read it.

I also know that there is no "profile merge" or mbox merge with deduplication. So again your chasing the non existent.

We could work with the original problem, but you appear to think you know what you are doing and find being asked to go back that far unsuitable to your needs. I guess you will just have to work it out then.