SolarWinds Backup - Modern server backup software
MailStore - MailStore Home - A 100% free single-private-user desktop solution
Datto Backupify - Protect your business with backup.
MailSteward - MailSteward : The Ultimate E-mail Manager for Mac OS X
Spanning Backup for Office 365 - Spanning Backup for Office 365 allows your organization to protect its critical Office 365 Mail, Calendar, OneDrive and SharePoint data. Specifically designed for Microsoft Office 365, Spanning makes backup effortless and recovery click-simple.
Gmvault - Backup the emails in your Gmail account.