Export your IMAP mail folders to MBOX using
eSoftTools IMAP backup & migration software and download it on your system now for more features. It is considered ideal for all users with its easy interface. It gives two solutions to the user, one is to create a single mbox file and save your IMAP mail folders in it and secondly, you can create separate mbox files for different IMAP mail folders and save them.
More info:- Export IMAP mail folder to MBOX