Compact a Personal Folder

Once a PST file gets to a certain size, it doesn't automatically compact.
This size varies and there's no explanation from Microsoft. Personal folders should then occasionally be compacted to help conserve space on the hard disk.

Solution:

To Check The Current Size Of The Personal Folders File

From the Folder List, right-click the Personal Folder and select “Properties”

2. Select the Folder Size button

3. The Total Size of the folder will be displayed in kilobytes.

Select the “Advanced” button

5. Select the Compact Now button to compact the file (the time it takes to compact will depend on how large the file is)

Once it's finished compacting, click the OK button twice to return to the main Outlook window

NOTE: Compacting has been known to run for several hours if the PST file is extremely large. If this is the case the compacting may be run on a lunch hour or after hours. Also, if the compacting is canceled at any time the Personal Folders will stay compacted up to that point. It's possible then to run the compacting over numerous days or so until it completes properly.