From time to time, you may get error messages when synchronizing your Offline folder (.ost) file in Microsoft Outlook with your mailbox on a Microsoft Exchange server. Or, you may notice that some items are missing from your .ost or from your mailbox after you synchronize the two.
Scanost.exe scans your .ost file and your mailbox on an Exchange server, comparing items and folders in each. If the tool finds any differences between the two sets of information, it will attempt to reconcile them. The tool records these 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'll need to fix manually.
Scanost.exe is installed when you install Outlook and is located at:
drive:\Program Files\Common Files\System\Mapi\1033\
For detailed information about running the tool, understanding messages it displays, reading the scan log, and manually resolving issues the tool couldn't resolve, see the readme file, Scanost.txt, at the same location.
Note The Inbox repair tool (Scanpst.exe) is another tool you can use to diagnose and repair errors in your .ost file. However, the Inbox repair tool scans only the .ost file, making sure that the file structure is intact. It doesn't scan your mailbox on the Exchange server. Use the Inbox repair tool if you have problems opening your .ost file. Use the .ost integrity check tool if you get error messages when you synchronize your .ost file with the Exchange server.