In Exchange 2010, you can use Multi-Mailbox Search to search mailboxes for e-Discovery or similar purposes. To preserve data in user mailboxes and protect its integrity, you can place a mailbox on Litigation Hold (also known as legal hold). This prevents mailbox items from being purged from the Store, without impacting user workflow. Additionally, when a mailbox is on litigation hold, a process known as copy-on-write (yes, COW) preserves a copy of the original item when a modification is made to certain item properties.
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