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Use the OST Integrity Check tool

If you get error messages when synchronizing your Offline Folder file (.ost) in Microsoft Office Outlook with your mailbox on a Microsoft Exchange Server, use the OST Integrity Check tool (Scanost.exe) to check your file. You must connect to your Exchange server so the tool can scan your mailbox folders and items. If you previously set up Outlook to automatically start offline, the OST Integrity Check tool won't be able to access your Exchange server. Therefore, before you run the tool, you need to temporarily change your startup settings.

1. Quit Outlook if it is running.
2. Double-click Scanost.exe, 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.
3. If you set up Outlook to prompt for a profile, the tool will also prompt you for one. In the Profile Name list, click the profile that contains the .ost you want to check.

   If you are prompted to Connect or Work Offline, click Connect.

4. Select the options you want.

   To have the tool automatically resolve discrepancies it finds during the scan, select the Repair Errors check box. If this check box is cleared, the tool will log the problems but not make the necessary corrections.

5. Click Begin Scan.

Note  To view the scan log, start Outlook, and then open the Deleted Items folder. The tool does not scan the Deleted Items folder. Any problems will be noted in a message with the Subject "OST Integrity Check."