When deleting a large number of Outlook items, especially emails from PST file, many users expect immediate changes to happen on PST file size. Unfortunately, deleting emails in an Outlook PST doesn’t mean that space will be freed up right away. It is not that how the concept of “deleting” works with Outlook!
“I archived and deleted a bunch of email messages in Outlook, in order to reduce the size of the PST file containing them. However, after doing so, the PST’s size is still the same. Outlook PST file size not reducing even after deleting emails. Can you explain what is happening?”
Well, there are two possibilities:
- Even after deleting Outlook items, you have to empty “Deleted Items” folder
- And a little patience is required after deleting
Now let’s understand these possibilities one by one.
Like Windows, your PST has an equivalent to the Recycle Bin called the “Deleted Items” folder. By default, when you delete an email message (or just about anything that Outlook stores in your PST), it’s not deleted at all, but simply moved to the Deleted Items folder.
Well, the idea of Deleted Items is to save you from disaster; a way to recover from “oops” moment when you didn’t mean to delete the item because things aren’t really deleted.
And of course, when things aren’t really deleted, there will be no free space!
The best part is you can make Outlook empty the Deleted Items folder when you exit Outlook, or you can simply empty it yourself. In the folder list, right click on the Deleted Items folder and click on “Empty Deleted Items” folder. This will permanently delete the items from your PST file.
But your PST won’t get shrunk. At least, not right away.
When Outlook actually deletes an email, the space taken up by that email is “freed”. Precisely, we can say that space within the PST is marked as unused, and made available for other email messages that might arrive thereafter. So your PST won’t get smaller right away, but it’s also quite likely that it won’t get bigger as new mail arrives either. The space freed within the PST by emptying the Deleted Items will simply get reused.
Further, Outlook is designed like a database and the space used by deleted items is not recovered until you shrink the database. Outlook may overwrite the now-unused space as new items are added to the PST, but the PST file needs to be compacted to recover space on the hard disk.
If you leave Outlook running, after some amount of idle time, it will start to perform something called ‘compaction’. Compaction is very similar to defragmenting your hard disk. During compaction, it moves all of the email messages and other “real” information in the PST to the front of the PST and moves all the unused or free space within the PST to the back. When compaction is done, Outlook can then actually make the PST file smaller by removing that portion of the PST that isn’t actually being used by anything.
Outlook won’t compact the PST file as soon as you move or delete Outlook items. It waits until there is 20% ‘white space’ (space used by the now-deleted items) and the computer is idle to begin compacting. When Outlook begins compacting, it may take several days to recover all of the space as it will stop when the computer is busy and restart when it’s idle.
Now that is where the patience comes into the picture! When you empty your Deleted Items folder, and just leave Outlook alone for a while, sometimes a long while, it will dutifully compact and shrink your PST.
However, if you don’t have patience, then you can manually perform Compaction process. To do this,
- In folder view, right click on Personal Folders
- Click on Properties for “Personal Folders”
- Click on the Advanced button
- Hit the Compact Now You’ll then see this small dialog for a while
Well, the time to free up space will depend on the size of your Outlook PST file. You may have to wait quite a while for large files.
Once it is completed, your PST will be freed up and will be small.
