imapsync - Console-based utility for migrating IMAP mailboxes.
Athena Archiver - Athena Archiver Email Archiving Solutions provide enhanced disaster recovery options by enabling automatic off-site email storage and data replication to a mirror site.
Gmvault - Backup the emails in your Gmail account.
Cryoserver - Cryoserver is an all-in-one email archiving solution that empowers you to preserve your email in a tamper-evident archive, making you transform your data into a useful archive for everyday use.
Archive2Azure - Archive360's email archive solution retains your data in your own cloud tenant. Say NO to proprietary email archive software that own your encryption keys.
Mail Backup X - Your one stop mail backup and archiving tool for Mac.