Outlook: Offline Folder (OST) issues

This article lists many of the ways in which you can troubleshoot an issue with the Outlook offline mail file. This file is often refered to as an OST.

Determine more about the issue:

• Record the error messages that are appearing.
• An error at the beginning that asks if you would like to start in online or offline mode indicates that Outlook believes there is a discrepancy between the information in the OST and the mailbox.
• Record the steps taken in order to receive the error condition. In some cases, the computer has to be shutdown, disconnected from the network and restarted before the OST issue will reveal itself.
• Have the user log onto another computer and perform the tests using the same version of Windows and Office if possible.
• Create a new test user with mailbox on the computer where the fault occurs, and see if the same issues occur.

Try the following steps to resolve an OST issue:

• Ensure the user has read/write access to the OST file location.
• Create a new profile and at the same time, change the location of the OST. If there is autoconfiguration involved, there may be a %username% in the location. Remove this and replace with a real path instead, as well as setting a name for the OST that does not already exist in that location. When it asks to create a new OST, click Yes. Finish the profile creation and set it to open when Outlook is next opened. The error message should generally be resolved by this step.
• Shutdown Outlook and rename the OST file. Restart Outlook and check if the issue reoccurs. Note: If the user has been writing to their OST and it has not been synchronised to the server, you will lose this information. Try to determine first if this is the case.
• Create a new Outlook profile.
• If the user is running Outlook 2003, you may try upgrading to Office 2007. This has been proven to resolve some OST issues (where the OST itself does not appear to be at fault).
• Try performing an uninstall and reinstall of Office. This has been proven to not resolve some OST issues.
• Empty out the deleted items folder. Deleted items may have become corrupted or too large.
• Remove any delegates on the mailbox. Delegates may have become corrupted and/or orphaned.
• Export any inbox rules and then delete what is there. Rules can become corrupted. These can be re-imported when testing is complete.
• Right click on a folder in Outlook and select properties. Select the synchronisation tab and check if the folder has synchronised successfully. If the synchronisation tab is not available then you may not be in cached mode. See KB842284. To synchronise all folders, press Send/Receive All. To synchronise just a single folder, select the folder and select Send/Receive this folder only.
• Replace the Exchange server service support files for Outlook. In Office 2007, rename the C:\Program Files\Microsoft Office\Office12\emsmdb32.dll. Go to Add/Remove Programs, select Reinstall or repair, then Reinstall. In Offce 2003 you should rename emsabp32.dll, emsmdb32.dll, emsui32.dll, then reinstall Office. See KB842284.
• Try running the OSTScan tool to check for corruption. Run without the automatic repair first. It will create a report in the deleted items folder. Check the report for issues. Rerun the tool in repair mode if required. See http://office.microsoft.com/en-us/outlook-help/scan-and-repair-corrupted-outlook-data-files-HA010075831.aspx?pid=CH100788841033#BM2
• Try moving the mailbox to a new Exchange server if this is an option.