Carbonite - Unlimited online backup for one flat fee. Free trial, no credit card required.
MailStore - MailStore Home - A 100% free single-private-user desktop solution
MigrateCloudData Office 365 Migration Tool - Office 365 Migration Tool is the most trusted software to migrate Office 365 data into another O365 and many other email clients.
MailSteward - MailSteward : The Ultimate E-mail Manager for Mac OS X
PieSync - Seamless two-way sync between your CRM, marketing apps and Google in no time
Gmvault - Backup the emails in your Gmail account.