In order to reduce disk consumption I deleted a large number of emails from Outlook and emptied the “Deleted Items” folder. I clicked the “Compact Now” button in the “File” menu > “Data File Management” > “Settings” to reduce the size of the data store files. However, the Outlook.pst file has remained the same size. How can I reduce the size of the PST file?

As you have deleted emails and then emptied the Deleted Items folder this should have decreased the size of your Outlook storage and compacting the PST file should have then decreased the size of the PST file itself. However, it seems that this has not occurred. To begin, we should make sure that you are looking at the correct PST files when checking their size. Outlook occasionally has a habit of creating multiple PST files, particularly if you have multiple Outlook profiles, so it is possible that the reason the size has not decreased is that you are not looking at the PST files which are used by your Outlook profile. In Outlook, right-click on the “Personal Folders” heading in the left-hand pane and select “Properties for Personal Folders”. The Properties window appears and you should click the “Advanced” button. That produces another window where you should see a field named “Filename” which is the full path to the PST file. Confirm that you have been viewing the correct PST file and looking at the file size.

Assuming that you have been looking at the correct file we should next check which folders within the PST file are taking up the most amount of space. Go back into the Properties for the Personal Folders file. In the Properties window that appears click the “Folder Size” button. A Folder Size window now appears where you can see the total size of the entire Personal Folders file together with the size of each individual Outlook folder contained within that Personal Folders file. Since you have compacted the PST file any email which was deleted from Outlook should have also been removed from the PST file so the current size of the PST file should be the leanest possible. Look through the listings of folders within the Personal Folders file to determine which folder is occupying the largest amount of space. Additionally, since you have emptied the Deleted Items folder this folder should be occupying a minimal amount of space. The fact your PST file has not changed size might be because the emails which you previously removed were quite small and there is still a significant number of large emails in Outlook (such as those with large attachments).

Once you have determined the Outlook folder or folders which are occupying the largest amount of space you will need to try to economise these folders further by removing email messages and then recompacting the Outlook PST file. This should allow you to reclaim some of the disk space which is being occupied by your email.

Assuming you have followed the steps to delete messages, emptied the Deleted Items, and then compacted the folders there is little else that can be done to reduce the size of the PST file since this is the exact procedure recommended by Microsoft to reduce the size of PST files (available at the following Microsoft Knowledge Base article support.microsoft.com/kb/289987). As a last resort, you could try installing the latest updates for Office to see whether that resolves the problem. You can update Office by visiting update.microsoft.com . Please let me know if you are still unable to reduce the size of the PST files.