If you're using Office 365, or one of the many hosted Exchange variants available today, you may be aware that MailStore has long been able to give you a complete and automatically synchronised off-site copy of your mail.
I've always been happy recommending it as a solution,
Office 365 outages happen so it is popular among our customers, however when my colleagues over in the German development team at MailStore let me know about their recent breakthrough in the latest version, I could immediately see the potential for hosted Exchange customers.