Exchange server users may be able to recover deleted items using Deleted Items recovery, if the administrator
has it enabled. If it's not enabled, they cannot recover items deleted from Exchange mailboxes.
How Outlook's Deleted Items folder works
A PST is a database. Items are records within the database and there is an index that points to each item. When you empty the Deleted Items folder, Outlook doesn't actually delete the items, it just deletes the items' listings from the index. The item is still in the PST, but unrecoverable because Outlook has no idea where it is without the pointer in the index. The space the item takes up is called "whitespace".
When you Compact a PST, the item is finally removed permanently and the whitespace is recovered, often shrinking the PST by many megabytes. Once the PST has 20% "whitespace", Outlook begins compacting the PST. If the Deleted Items folder contained a lot of messages, Outlook may begin compacting the PST immediately and the items will be deleted forever within a few minutes.
To recover the items which are no longer in the index you need to force Outlook to rebuild the index by causing corruption. You can cause corruption by using a Hex editor to delete some characters from the beginning of the PST file. If you delete the wrong ones you'll cause corruption but not in the index and Outlook won't rebuild the index.
Recover the Deleted Items
If you don't know what a Hex editor is, you probably shouldn't be hex editing anything, but if you want to try, Google for "hex editor" - UltraEdit is probably the best and easiest one to use. Before doing anything to the PST with a Hex Editor, make a copy of the PST, or you may end up losing all of your e-mail.
1.Open the PST in the Hex editor.
2.Delete positions 7 through 13 with the spacebar. Since you're using hexadecimal numbering, this actually clears 13 characters in the following positions:
00007, 00008, 00009, 0000a, 0000b, 0000c, 0000d
0000e, 0000f, 00010, 00011, 00012, 00013
As you clear the characters, the editor displays the code “20” in their position.
3.Save the PST, it is now corrupted.
4.Run the Inbox Repair Tool, SCANPST.exe, to recover the file. Use Windows Search utility to find it.
5. The Inbox Repair Tool creates a backup and repairs the damage and recreates the PST.
Open the new PST in Outlook. The Deleted Items folder should now contain the deleted messages, unless Outlook has already deleted them for good by compacting the PST.