Gmvault - Backup the emails in your Gmail account.
Thexyz - Secure premium email service with mobile sync apps for calendar, contacts, tasks, notes and FISMA compliant email archiving.
SysTools Gmail Backup - Backup Gmail Emails, Contacts, Calendar, and Google Drive Storage File by SysTools Gmail Backup Solution
ZixArchive - ZixArchive is a cloud-based solution to collect, store and search archived emails.
MailStore - MailStore Home - A 100% free single-private-user desktop solution
Barracuda Message Archiver - Barracuda Message Archiver is an application that enables you to retrieve and retain all email communication while reducing storage recommendations.