Read time 5 minutes

Summary: The article addresses OST synchronization issues in Exchange. It discusses causes, troubleshooting methods, and tools. It emphasizes the importance of resolving issues and recommends Kernel for OST to PST Converter for recovery.

Ensuring smooth offline functionality in the Exchange environment relies heavily on synchronizing Exchange mailboxes with their offline counterparts on user machines. Unfortunately, numerous Outlook users encounter error messages or encounter problems when the synchronization of their OST file (Offline Outlook Data File) encounters issues. In this context, we will explore prevalent OST synchronization problems and how to resolve them.

How Does the Synchronization Between OST and Exchange Server Work?

The Outlook application synchronizes the OST file with the Exchange Server mailbox when there is an active Exchange connectivity. The synchronization speed can vary among different Outlook versions, influenced by the volume of data being processed.

Why Exchange OST Synchronizations Issues?

In most cases, the synchronization between the Exchange server and Outlook proceeds smoothly. However, occasional disruptions may occur, primarily driven by factors such as poor network connections or hardware issues. The failure of Exchange OST synchronization can also be attributed to the corruption or damage of OST files.

Exchange OST Synchronization Errors – How do They Appear?

Synchronization problems with Exchange OST can disrupt Outlook users in various ways:

  • At the time of Exchange synchronization, you get an error message:Cannot start Microsoft Outlook. Cannot open the Outlook window. The set of folders cannot be opened. The file xxx.ost is not an Outlook data file (ost).
  • You have Outlook issues when Cached Exchange Mode is enabled, but no issues when it is disabled
  • Some mailbox items (email, contacts, etc.) are missing after synchronization of OST file with the Exchange Server You see item mismatch while accessing the same mailbox in Outlook and Outlook Web Application

(For older Outlook versions 2010, 2007, 2003)
Even if you aren’t encountering any specific errors but have a sense that the offline file is not syncing with the Exchange Server, you can employ some fundamental troubleshooting methods to investigate potential synchronization issues.

  1. Go to any mailbox folder which is not synchronizing. Right-click and select its Properties.
  2. Go to synchronization tab and if there is no synchronization tab, then it means that you have not set up the folder for using in the offline mode.
  3. In the statistics for this folder, check the multiple details like Last Synchronized on, server folder contains, offline folder contains.
  4. When there is a solid connection between Outlook and Exchange, and folder synchronization is successful, the server folder and the offline folder will contain identical details. However, if there are discrepancies, it indicates that the details between the two are not in sync.
Automatic synchronization

For the automatic synchronization, follow the below steps;

  1. Click Tools, then Options.
  2. Under the Mail Setup tab, go to Send/Receive tab and click the checkbox for Send immediately when connected.
  3. Click Send/Receive.
  4. Check that the Perform an automatic send/receive when exiting option is clicked under the Send/Receive Groups dialog box.
  5. Click OK.
Which all Versions of Outlook are Affected by OST Synchronization Issues?

All versions of Outlook are affected by OST synchronization issues, including Outlook 2019, 2016, 2013, 2010, 2007, & 2003.

How to resolve OST Synchronization issues?
  • OST Integrity Check Tool
    The OST Integrity Check tool (Scanost.exe) is designed for use with Outlook 2003 and Outlook 2007 versions. Since this tool is not applicable to recent versions of Outlook, we won’t delve into it in detail.
  • Manual synchronization of offline folders (for Outlook 2010, Outlook 2013, & Outlook 2016)
    This method is effective for addressing synchronization issues at the folder level. If you encounter synchronization problems with specific folders, consider the following approach:
    a )Right-click on the OST folder and click Properties.
    b )Click on Clear Offline Items; click OK.

    c )Click the Update Folder button in the Send/Receive tab

    Update Folder

  • Use the Inbox Repair tool
    The Inbox Repair Tool (scanpst.exe), also can be used to scan and repair damaged OST files.
    Read more…
  • Rebuild the OST file
    If OST issues are still persistent, you can rename your affected OST file and let Exchange rebuild the OST file.
How to Rebuild the OST File?

To build a new OST file, follow:

  • Close the Outlook application.
  • Go to the location C:\Users\administrator\AppData\Local\Microsoft\OutlookGo to the Outlook location
  • Find the OST files (For eg: Outlook.ost, Oultook0.ost, Outlook1.ost, etc.) and rename them (deletion is not recommended as you may have to recover some unsaved data from this file later).
  • Restart Outlook, and wait till the mailbox gets synchronized.Restart Outlook

When you delete or rename the old OST file and create a new one, you might discover that certain data is missing from the original OST file. This can occur when some work hasn’t been saved to the Exchange mailbox from the OST files. In such situations, you can turn to a reliable OST recovery application to recover the entire mailbox from the OST file. One option to consider is Kernel for OST to PST Converter, which is capable of retrieving even unsaved work from the old OST file.


All the methods outlined in the article are valuable for addressing various synchronization issues between the Exchange Server and its OST data file. However, in cases where the OST file is corrupted and displays errors, manual synchronization may not be possible. To recover a corrupt OST file, it is recommended to utilize Kernel OST to PST software, as it is capable of eliminating errors and restoring the complete file. Subsequently, you can synchronize the recovered items into a new PST file and utilize it within Outlook.

Kernel for OST to PST