You can perform a hard delete of a message by highlighting the message and pressing Shift+Del. Performing a hard delete removes the message without moving it to the Deleted Items folder. When you attempt to recover hard-deleted items, you’ll see that the hard-deleted messages aren’t listed in the recovery dialog box. If you select the folder from which you performed the hard delete (e.g., Inbox), you’ll see that the option to recover deleted items is grayed out on the Tools menu.
You can recover items that have been deleted from an Outlook folder–including hard-deleted items–either by performing the following steps or by adding the dumpster.reg entry to the registry. (You can download the dumpster.reg entry at dumpster.reg.)
1. Start the registry editor (regedit.exe).
2. Navigate to the HKEY_LOCAL_MACHINESOFTWAREMicrosoftExchangeClientOptions 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. Click OK.
6. Close the registry editor.
When you restart Outlook, the option to recover messages should be available for all folders.