Gmvault - Backup the emails in your Gmail account.
Barracuda Email Protection - Barracuda Essentials offers advanced Office 365 security features including email scanning, archiving, backup & recovery, and real-time phishing defense.
Datto Backupify - Protect your business with backup.
Athena Archiver - Athena Archiver Email Archiving Solutions provide enhanced disaster recovery options by enabling automatic off-site email storage and data replication to a mirror site.
MailStore - MailStore Home - A 100% free single-private-user desktop solution
Thexyz - Secure premium email service with mobile sync apps for calendar, contacts, tasks, notes and FISMA compliant email archiving.