The wiki page which mentions mdbox talks about a "cleanup" step for mdbox:
: The space is later freed in "cleanup" step. This may be done : automatically within the session or later in a nightly cronjob when : there's less disk I/O. The cleanup first finds all files that have : refcount=0 mails. Then it goes through each file and copies the : refcount>0 mails to other dbox files (to the same files as where newly : saved messages would also go), updates the map index and finally : deletes the original file. So there is never any overwriting or file : truncation.
I was wondering if there was any code to actually do this, or any command-line tools (and if either of those where they might be), or whether it was just design musings at the minute.
Regards,
Bill