From time to time, you may get error messages when synchronizing your Offline Folder file (.ost) (Offline Folder file: The file on your hard disk that contains offline folders. The offline folder file has an .ost extension. You can create it automatically when you set up Outlook or when you first make a folder available offline.) in Microsoft Office Outlook with your mailbox on a Microsoft Exchange Server. You may also notice that some items (item: An item is the basic element that holds information in Outlook (similar to a file in other programs). Items include e-mail messages, appointments, contacts, tasks, journal entries, notes, posted items, and documents.) are missing from your .ost file or from your mailbox after you synchronize your .ost file and mailbox. When this occurs or you have other problems synchronizing, you should use the OST Integrity Check Tool (Scanost.exe) to check your .ost file.
The OST Integrity Check Tool runs only on .ost files and can be used to diagnose and repair synchronization issues. It scans your .ost file and your mailbox on an Exchange server, comparing items and folders in each, attempting to reconcile synchronization differences between your mailbox on the Exchange server and your local copy of the .ost file. It doesn't change your mailbox on the Exchange server. The tool records any differences in a scan log so that you can see what discrepancies it found and resolved. The scan log also identifies any situations the tool couldn't correct that you will need to fix manually. The scan log can be found in your Deleted Items folder.
If you have problems opening your .ost file, you can use the Inbox Repair tool (Scanpst.exe) to diagnose and repair errors in your .ost file. The Inbox Repair tool (Scanpst.exe) can be used on both .ost files and Personal Folders files (.pst) (Personal Folders file (.pst): Data file that stores your messages and other items on your computer. You can assign a .pst file to be the default delivery location for e-mail messages. You can use a .pst to organize and back up items for safekeeping.). The Inbox Repair tool scans the .ost or .pst file, making sure that the file structure is intact. It does not interact with your mailbox on the Exchange server in any way.
The OST Integrity Check Tool (Scanost.exe) is installed when you install Outlook and is located at:
drive:\Program Files\Common Files\System\MSMAPI\LocaleID folder - where LocaleID is the locale identifier (LCID) for the installation of Microsoft Office. The LCID for English - United States is 1033.