Office 365: Recover deleted email from a shared mailbox

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

Outlook 2013 option to recover deleted items greyed out


You can use the DumpsterAlwaysOn registry in order to be able 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
  • Key for 64-bit Outlook on a 64-bit version of WindowsHKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Exchange\Client\Options

Create a new DWORD value with the name of DumpsterAlwaysOn and set the value to 1.

On my own system (Windows 7 64-bit with Outlook 2013) the “Options” key was not present and I had to create it first before adding the DumpsterAlwaysOn DWORD.

Setting DumpsterAlwaysOn in the registry to enable Outlook to recover hard deleted items.


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:

Enabling the option to Recover Deleted Items in Outlook 2013 using the DumpsterAlwaysOn registry value


Recover Deleted Items for non-mail folders in Outlook 2010

Even though the Recover Deleted Items feature works for all non-mail folders in Outlook 2010, the feature is not available by default on the Folder tab for these type of folders. So if you have deleted a task or a calendar appointment and need to recover it, here is how to do it.

  1. Go to File, then Options
  2. Choose “Quick Access Toolbar”
  3. Change the “Choose commands from” list to  “All Commands”
  4. Select “Recover Deleted Items…” from the list
    How to add the "Recover deleted items" option to the Outlook 2013 quick access toolbar
  5. Click on the “Add > >” button.
  6. Click OK.

You should then have a new option on your quick access ribbon that will enable you to recover deleted items from any folder that contains items that can be recovered.

The recover deleted items quick access toolbar icon

Microsoft have some more information and a “Fix it for me” procedure on their website:

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Convert from 512 byte blocks to Megabyes and Gigabytes

It’s pretty common for me to have to make size conversions between 512 byte blocks and something more readable, such as Megabytes or Gigabytes. I’ve got a simple formula to do the conversion.

How to convert 512k byte blocks to Megabytes or Gigabytes

In simple terms the formula to convert from 512 byte blocks to megabytes is:

Number Of 512 byte blocks/2/1024

and to Gigabytes it is:

Number Of 512 byte blocks/2/1024/1024

The reason that I am making this calculation is because I often work on IBM AIX, the default output of the du command is in 512 byte blocks. I believe this is a POSIX standard.  But it is really not easy to read at a glance. Recent versions of AIX have an option on the df command to produce human readable output, but I sometimes work on ancient versions.

So for my own sake as much as anyone else’s I quickly wrote this little converter so that in future I don’t need to refer to the formula above and can just quickly get the result.

Converter for 512k byte blocks

Simply enter the output provided by the df command into the textbox below and the sizes in Megabytes and Gigabytes will be displayed.

Number of 512 byte blocks

Value in Megabytes:
Value in Gigabytes:

Hope this helps someone, I know it will help me!

If you want more information on how to do these conversions, there is a really good article on it by Brian Smith on his blog: