MailStore - MailStore Home - A 100% free single-private-user desktop solution
imapsync - Console-based utility for migrating IMAP mailboxes.
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.
MozBackup - Backup tool for Firefox and Thunderbird
Hornetsecurity Email Archiving - Hornetsecurity Email Archiving is one of the advanced software that offers long-term, unchangeable, and secure storage of important company information, data, and flies.
Gmvault - Backup the emails in your Gmail account.