Gmvault - Backup the emails in your Gmail account.
imapsync - Console-based utility for migrating IMAP mailboxes.
MailStore - MailStore Home - A 100% free single-private-user desktop solution
SpinBackup - Spinbackup is the most comprehensive SaaS Data Backup & Security solutions provider for G Suite. Try our 15-Day Free Trial Today!
Fetchmail - The Fetchmail Project
Datto Backupify - Protect your business with backup.