The Outlook e-mail client provides a broad range of functionality that manages information in the background through the use of "data files" that are essentially databases that organise user information and messages. If you notice Outlook performance is lagging, it could be that the "data files" (which includes the OST file) are fragmented, causing Outlook to search longer to find requested information. To resolve the issue and restore acceptable performance to Outlook, "defrag" the OST file.
Close the Outlook program.
Click the "Start" button, then click the "Search" box. Type "*.ost" in the "Search" box and press the "Enter" key. Right-click the "OST" file displayed in the search results and click "Properties" in the menu that appears.
Note the path to the "OST" file that is displayed in the "Properties" window that appears.
Click the "Start" button, then click "Programs." Click "Accessories" and then right-click on the command line icon. Click "Run as Administrator" in the menu that appears.
Type "cd c:\path_to_contig," substituting "c:\path_to_contig" with the actual path and directory where the Contig utility is located, then press the "Enter" key.
Type "contig --v path_to_ost/filename.ost," substituting "path_to_ost/filename.ost" with the actual path and name for the "OST" file, then press the "Enter" key.
Wait while the Contig utility processes the "OST" file. When the command line output confirms that the defrag operation has completed, you can start Outlook.