E-mail servers like Qmail store messages received for their users in mailboxes with a directory structure called maildir.
E-mail clients like Mozilla Thunderbird can import messages in mailbox files but these must be in mbox format, which consists in a single file with all the messages in the mailbox.
This class provides a solution that makes possible to take messages stored in mailboxes in the maildir format and export the messages in single files in the mbox format.