The Exchange server stores all deleted items for up to three days before purging them. To retrieve any such items, carry out the following steps on a Windows machine running Microsoft Outlook 2003 or 2007:

1. Start the registry editor, regedit.exe, by select Start >> Run >> regedit
2. Navigate to the HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Exchange\Client\Options subkey.
3. From the Edit menu, select New and click DWORD value.
4. Enter the name DumpsterAlwaysOn and press Enter.
5. Double-click the new value and set it to 1.
6. Click OK.
7. Close the registry editor.
8. Start Microsoft Outlook.
9. Select the folder (e.g. Inbox) from which the messages disappeared by clicking on its icon in the left folder list.
10. Choose Recover Deleted Items from the Tools menu.
11. Select the item(s) you want to recover and click on Recover Selected Items.

The item(s) will then reappear in the Inbox and/or folder you selected.