Outlook - Accepting Outlook invites deletes other inbox message

I use a web-based email program. Today, someone sent me a meeting invitation from Outlook. I accepted it, and when I clicked back to my inbox, another completely separate and very important email had been deleted from my inbox. The meeting request is still there, but this other message is gone. It is not in my deleted items folder, nor is it in any of my other folders. This message is vitally important, is there a way to get it back?

You have hard deleted (permanently deleted) items in Outlook and want to recover them. For example, if you do not move items to the Deleted Items folder before you delete them, these items are hard deleted, and you cannot recover them from the Deleted Items folder.

By default, the Recover Deleted Items functionality is only enabled on the Deleted Items folder in a user's private folders. Items that are hard deleted cannot be recovered. To enable the Recover Deleted Items functionality on mail folders other than the Deleted Items folder (for example, for the Sent Items, Drafts, Outbox and Inbox folders), make the following changes to the registry:

1. Start Registry Editor.
2. Locate and then click the following key in the registry:
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Exchange\Client\Options
3. On the Edit menu, click Add Value, and then add the following registry value:
   Value name: DumpsterAlwaysOn
   Data type: DWORD
   Value data: 1
4. Close Registry Editor.

You can use an administrator's computer or a user's computer to make this change to the registry. After you change the registry, start Outlook, and then click Deleted Item Recovery on the Tools menu. A list of items that were hard deleted during the retention time that is set on the server is displayed.


MSDN

Note this may not work if

If your Exchange server is not configured to keep deleted items, the Fix this problem button or the steps to change the registry do not work. This solution requires you to use a Microsoft Exchange Server 2000 account, an Exchange Server 2003 account, or an Exchange Server 2007 account. Most home and personal accounts do not use Microsoft Exchange.