[Dovecot] Integrate mbox into mdbox

Hi! I have several mbox files (unstructured, only the big plain mbox files) and I would like to integrate/read these mbox files into mdbox subfolders of specific users.  This is a production system and I don't want to disturb running services and I am a bit afraid of not using the right command and maybe destroying (or whatever) their mailboxes.  I am sure it is pretty easy.  Can someone please tell me the correct dsync command line that I should use to read each mbox file (one-way) into the specific folder of the mdbox folder structure of a specific user? Thanks a lot, -lutzn