If you have hard deleted (Shift-delete) a message or mail-item from a shared mailbox you may notice that the option to recover deleted items is greyed out and you cannot select it.
Hard deleted items can be restored from your deleted items folder quite easily but this option is not available in certain circumstances or for certain folders, including folders in shared mailboxes. The default deleted item retention in Office 365 is 30 days.
Recover Deleted Items Greyed out
You can use the DumpsterAlwaysOn registry in order to be able to recover deleted items.
Setting the DumpsterAlwaysOn Registry Value
As stated above, if you find that the “Recover Deleted Items” option is grayed out then you need to set the DumpsterAlwaysOn Registry value.
- Key for 32-bit Outlook on a 32-bit version of WindowsHKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Exchange\Client\Options
- Key for 32-bit Outlook on a 64-bit version of Windows HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Exchange\Client\Options
- Key for 64-bit Outlook on a 64-bit version of WindowsHKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Exchange\Client\Options
Note: Depending on your Windows and Outlook versions, if the “Options” key is not present, you will need to create it first before you can add the DumpsterAlwaysOn DWORD.
After you have made this change, you need to restart Outlook for the changes to take effect and then you should see the option become available:
Microsoft has some more information and a “Fix it for me” procedure available at: https://support.microsoft.com/en-us/help/246153/how-can-i-recover-items-that-i-have-hard-deleted-in-outlook