Users often delete data from their mailboxes that they later want recovered. Recovery of these deleted items is the most common reason for IT admins to recover data from traditional point-in-time backups today.

With previous versions of Exchange Server, administrators implemented two solutions to enable single item recovery, dumpster and restores.  Both had their issues, unfortunately. 

Exchange 2010 aims to reduce the complexity and administrative costs associated with single item recovery.

Terminology

The following definitions may be useful for understanding the content within this article:

  • Store Soft Delete - this is when an item has been deleted from the Deleted Items folder and placed within dumpster.
  • Store Hard Delete - This is when an item has been marked for purging out of the store.
  • Hard Delete via Outlook (Shift-Delete) - This is when the end user performs a shift-delete on an item.  This results in the item bypassing the deleted items folder and being directly placed in dumpster.

Single Item Recovery in Previous Versions of Exchange

The end user single item recovery functionality was enabled through the store via the store dumpster.  Administrators configured the dumpster setting on a per database or per mailbox basis.  The default deleted item retention window in Exchange 2003 is 7 days, while with Exchange 2007 the default is 14 days. 

The rest of it is there :

http://msexchangeteam.com/archive/2009/09/25/452632.aspx