Now there is a free solution available for users to export IMAP mail folders to MBOX files, called
eSoftTools IMAP Backup & Migration software. This software is able to download IMAP emails to MBOX and many other file types. It also allows to migrate emails from one IMAP email account to another. Also, allows to create separate folders for saving IMAP mails on IMAP server. It is available for all Windows versions (up to Windows 11). So try it now.
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How to Download & Export IMAP Mail folder to MBOX files