Microsoft released a quick fix for a nasty bug in Outlook 2013 Preview, part of the Office Professional Plus 2013 Preview. The related knowledgebase article is kb2737132.
Note: Despite the warning that goes with pre-release software about not using it in production environments, I assume Microsoft knows people will and decided to produce a hotfix so quickly, which is quite unusual for preview software, also looking at the potential consequences.
The bug causes everything, i.e. e-mail, contacts, appointments and tasks, to be deleted permanently from an Exchange server when using the Cleanup Tools from Outlook. Nothing is recoverable through the Recover Deleted Items option.
To install the hotfix, follow one of the links below, depending on your architecture: