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.

I hope you found the information useful and Thank you for reading.