There are many software in the world and people are confused about which one is right for exporting their emails, so I would recommend you to use
eSoftTools IMAP backup & migration software. With the help of this, you can easily export IMAP mail folders to mbox. It gives two options to the user, they can save all IMAP mail folders in one mbox file and can also create separate mbox files to save different IMAP mail folders. Many new file formats are available in this single software to save IMAP emails and the good thing is that it has both Hindi and English versions. Read the free demo for more information.
Read more:- Export the IMAP mail folder to MBOX