Achieving Immutability with Exchange Online and Exchange Server 2013 é o mais recente white paper técnico disponível para download no website da Microsoft.
The Principle of Immutability
For many organizations, regulatory compliance, internal governance requirements, or litigation risk require the preservation of email and associated data in a discoverable form. All data in the system must be discoverable, and none of it can be destroyed or altered. The industry-standard term for this is “immutability.”
Traditional methods of achieving immutability have typically worked by moving email messages to a separate, read-only storage location. While such systems serve the purpose of preserving mailbox items for discovery, they often affect the user experience in significant ways by removing preserved items from the customary daily workflow. For IT professionals, this approach to immutability requires the deployment and ongoing maintenance of a separate server and storage infrastructure. Discovery itself is performed with tools external to the mail system, with associated deployment and maintenance costs.
Brief Description
With Exchange Server and Exchange Online, Microsoft enables organizations to immutably preserve mailbox items for eDiscovery using an in-place strategy.
Overview
With Exchange Server and Exchange Online, Microsoft enables organizations to immutably preserve mailbox items for discovery using an in-place strategy, keeping those items within the Exchange infrastructure. The technology used to achieve immutability with Exchange is different than sending items to a separate, read-only archive. The Exchange approach achieves the same or better results—preserving all inbox data in a way that is tamper-proof and discoverable—while at the same time conserving more of the relevant data, reducing IT complexity, and delivering a seamless user experience.
A Microsoft disponibilizou uma série de guias Work Smart, dos quais gostaria de destacar 
