If you delete items from a Personal Folders file (.pst) , the size of the file will not change unless you compact the file. The procedure to compact the data file might take several minutes.

1. On the File menu, click Data File Management.
2. Click the data file that you want to compact, and then click Settings.
3. Click Compact Now.

 Note    You do not have to exit Microsoft Office Outlook after you compact a .pst file.