When you delete an email in Outlook – it really isn’t deleted; it’s only “marked” for deletion. It’s only until you “compact” your PST file that your email is permanently erased, and the empty space is reclaimed.
Outlook’s Inbox Repair Tool (ScanPST.exe) can diagnose and repair errors in your PST file. If the file is not corrupt, it does some minor clean-up – but if the file IS corrupt it also reverts all objects to “not deleted.”
So we’ll first need to “corrupt” your PST file to have ScanPST reclaim your “deleted” emails. [NOTE: I'm not including detailed instructions. If you're not comfortable please ask someone to help you.]
1) Locate and backup your Outlook PST file
2) From the Command Prompt type
f 107 113 20
3) Now that you’ve “corrupted” your PST file run ScanPST (usually found in C:\Program Files\Common Files\System\Mapi\1033)
4) Once ScanPST completes, your deleted emails will be restored.