I started working on this script last year and had the opportunity to put it to the test in May 2021 when migrating the Spip mailing lists. The script is still very young but I’m now confident that it is usable.
There still are many manual steps involved in the import and I would love to have something like discourse import --mailman2 config.pck mbox-archives-directory that would “just work”. However I don’t plan to implement this. I’m happy with custom shell scripts and I don’t see how they could be generalized. In any case the logic implemented by mailman2discourse is one piece of the puzzle that was missing and I’m happy it exists 