A recent bug in Google Apps allowed students to read each other's email. Read about it here.
Imagine if your company and your competitor were both on Google. Now imagine stumbling across your competitor's inbox. Whoops!
This underscores the importance of security whenever multitenancy is employed for email hosting. And it lends credence to customer concerns to have all their email encrypted when in the cloud.
And while this article applies to Google, the same could happen with Microsoft or any other vendor hosting multiple companies on a common infrastructure.
... David Sengupta