Currently Thunderbird uses mbox as primary storage format for mails (locally). All the mails in a folder are stored in the same file with the same name as the folder and no extension. The messages are separated from each other by a "From - " line. The maildir format is also supported, but there is no converter for it yet. The goal is to implement a component to migrate a store from the mbox format to maildir format. In order to achieve the goal a new store should be created and all the messages from all the folders of the old store should be moved to respective folders of the new store in maildir format. The folder hierarchy of the old store needs to be maintained in the new store. The message copying should be carried out in a worker using OS.File to prevent other tasks from getting locked up for long.