MailStore - MailStore Home - A 100% free single-private-user desktop solution
MigrateEmails IMAP Backup Tool - MigrateEmails IMAP Backup Tool is an efficient tool to easily backup IMAP emails to PST, MBOX, Gmail, G Suite, etc
MozBackup - Backup tool for Firefox and Thunderbird
isync (mbsync) - mbsync is a command line application which synchronizes mailboxes.
imapsync - Console-based utility for migrating IMAP mailboxes.
Softaken IMAP to IMAP Migration - Softaken IMAP to IMAP Migration allows transfer of emails from one IMAP Server to another. All IMAP Servers are compatible with this application. Users can easily migrate complete mailbox folders between IMAP Server accounts with attachments.