Q: How do I repair an .ost file offline if there's no scanost.exe in Outlook 2010?

A: As I wrote in "What Features Were Removed for Outlook 2010?" the Offline Folders file (.ost) integrity check tool, ScanOST (scanost.exe), was removed when Microsoft Outlook 2010 was shipped. What do you do when you're experiencing problems, such as minor mailbox synchronization issues or missing items, with Offline Folders in Outlook 2010?

Ideally, you do the same thing you've always done: You delete the local .ost file and have Outlook rebuild it from scratch when you recreate the connection to the Microsoft Exchange Server in the user's profile. Offline Folders, after all, are just a local Outlook copy of an Exchange mailbox. ScanOST was an option before Outlook 2010 and was used only on .ost files. It helped with the same issues as ScanPST (scanpst.exe), as well as server synchronization problems.

But what if you're really offline and you're having problems with your .ost file, such as items seemingly missing or inaccessible? First, the content on the server remains, so you essentially have a backup. Your .ost file, however, could hold substantial content that you haven't yet synchronized with the server and that you don't wish to lose. ScanPST is still available and can be run against .pst files and .ost files. ScanPST doesn't need access to an Exchange mailbox, as ScanOST does, although it doesn't check synchronization issues.

The first step in checking your offline .ost file would be to export the contents to a .pst file as a backup. The Import and Export option in Outlook 2010 isn't located in the most intuitive place. You'll find it at File, Open, Import, as Figure 1 shows.

Figure 1: Outlook 2010's Import option
Figure 1: Outlook 2010's Import option (Click image for larger view)

Exporting to a .pst saves a backup of your .ost, including changes you've made since your last synchronization. Then you run scanpst.exe against your .ost file.

Scanpst.exe is located in \Program Files\Microsoft Office\Office14 (or \Program Files (x86)\Microsoft Office\Office14 for 32-bit Outlook installed on 64-bit Windows). If ScanPST reveals errors, you should let the utility attempt to repair them. If the .ost file isn't reparable, you'll have to recreate the .ost when your Exchange Server is again available, and then import the .pst content back into the mailbox. During the import, you can select the option to exclude duplicate items so you only import the backed up content that was generated after the last mailbox synchronization and before the export to .pst was performed.