imapsync - Console-based utility for migrating IMAP mailboxes.
Gmvault - Backup the emails in your Gmail account.
MigrationWiz - MigrationWiz provides on-demand mailbox migration services through a fully automated cloud-based...
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.
Fetchmail - The Fetchmail Project
Mail Backup X - Your one stop mail backup and archiving tool for Mac.