MailStore - MailStore Home - A 100% free single-private-user desktop solution
imapsync - Console-based utility for migrating IMAP mailboxes.
isync (mbsync) - mbsync is a command line application which synchronizes mailboxes.
MozBackup - Backup tool for Firefox and Thunderbird
MigrateCloudData IMAP Mail Backup Tool - A trusted software with better designs and functions to perform the backup and migration of IMAP emails.
Gmvault - Backup the emails in your Gmail account.