I'd disagree with this lesson. Saying "do not utilize cloud solutions" period is nuts. Google and Microsoft are way better at email hosting and delivery than your on-prem server is unless you spend a ton more money on hardware and engineers to keep it up, which is simply not worth it for many companies. Dropbox is going to have better uptime and lower TCO than your self-hosted owncloud instance.

What I will say is it's important for the customer to HAVE THEIR OWN BACKUPS. Don't rely on the vendor - that's the lesson here. If you have all your stuff in AWS back that data up someplace that's not AWS, etc.