An Outlook Offline Storage Table (OST) file is a local copy of your Exchange mailbox that allows you to access and work with your emails, calendar items, contacts, and other mailbox data even when you are offline. It regularly synchronizes with the Exchange server to keep your local mailbox data up to date while also allowing you to access and work with mailbox items when an internet connection is unavailable.
However, sometimes you encounter an issue where the Outlook OST file is not synchronizing with Exchange. When this happens, Outlook may fail to update your mailbox data with the latest emails, calendar changes, contacts, and other mailbox updates. You may notice that Outlook continues to display older messages, emails remain stuck in the Outbox, or changes made in Outlook are not synchronized with your Exchange mailbox.
In this article, we will discuss the common reasons for the OST not syncing with Exchange issue and how to fix it.
Common Reasons Why Outlook OST File is not Syncing With Exchange Server
There are several reasons that can cause the OST not syncing issue. Some of the most common are listed below:
- Network connectivity is poor, unstable, or unavailable
- Work Offline mode is enabled
- Cached Exchange Mode is disabled or not working properly
- The OST file is damaged or corrupted
- The Outlook application is outdated
- The mailbox is full or has reached its storage limit
- The Exchange server is down or experiencing problems
- The Outlook profile is corrupted
- Authentication fails because of incorrect or expired credentials
Synchronization errors occur in specific folders
How to Fix Outlook OST File is not Syncing with Exchange Server?
Sometimes, Outlook synchronization issues are caused by temporary application glitches. You can restart Outlook to clear temporary processes that may be interfering with mailbox synchronization. If you still encounter the issue, you can try the following the solutions:
Method 1: Check the Outlook Connection Status
The first step is to check whether Outlook is properly connected to the Exchange server. Outlook needs an active connection to Exchange to send and receive emails and synchronize changes made to your mailbox. If Outlook is disconnected, new emails may not appear in your Inbox, messages may remain in the Outbox, and changes made to folders may not be updated on the server. As a result, Outlook may fail to synchronize the latest emails, calendar updates, contacts, and other mailbox changes between the OST file and the Exchange server. Follow the steps below to verify the connection status of Outlook:
- Open Classic Outlook on your computer.
- Check the status message at the bottom of the Outlook window. Look for messages such as Connected to Microsoft Exchange, Disconnected, Working Offline, or Trying to connect.
If Outlook displays Working Offline, select the Send/Receive tab.
- Click Work Offline to disable offline mode, then wait for Outlook to reconnect to the Exchange server and synchronize your mailbox.
If the status continues to show Disconnected or Trying to connect, check your internet connection and try signing in to your organization’s webmail through a browser. If you can access your mailbox through webmail but Outlook remains disconnected, the issue may be related to the Outlook client, Outlook profile, or Outlook connection settings.
Method 2: Check Cached Exchange Mode Settings
Cached Exchange Mode allows Outlook to create and use an OST file to maintain a synchronized copy of your Exchange mailbox on your computer. If this mode is disabled, Outlook cannot use the OST file to store and synchronize mailbox data locally, which may cause the OST file not syncing with Exchange issue. synchronization issues between Outlook and the Exchange server. To fix this issue, you can enable Cached Exchange Mode and check if the OST file is syncing with Exchange. Follow the steps below to do so:
- Open Classic Outlook.
- Select File > Account Settings > Account Settings.
- On the Email tab, select your Exchange or Microsoft 365 account, and then select Change.
- Verify that the Use Cached Exchange Mode option is enabled. If it is disabled, enable it.
- Review the Mail to keep offline slider, if available, and select the desired synchronization period.
Select Next to save the changes. If prompted, restart Outlook for the changes to take effect.
Method 3: Check the Send/Receive Settings
Classic Outlook uses Send/Receive settings to determine how often it checks for new emails and which folders it updates during synchronization. If automatic Send/Receive is disabled, Outlook may not check for new messages at the scheduled intervals. Similarly, if a folder is excluded from the relevant Send/Receive group, Outlook may not update that folder through the scheduled process. This can delay the appearance of new emails and other mailbox changes in Outlook and its locally cached OST file.
Follow these steps to review the Send/Receive settings in Classic Outlook:
- Open Classic Outlook.
- Select Send/Receive > Send/Receive Groups > Define Send/Receive Groups.
- In the Send/Receive Groups window, select All Accounts or the relevant group.
- Under Setting for group, check whether Schedule an automatic send/receive every _ minutes is selected. If you want Outlook to check for updates automatically, enable this option and set an appropriate interval.
- Select the relevant group and click Edit to review its account and folder settings.
- Select your email account and verify that Include the selected account in this group is enabled, if this option is available.
- Review the folder settings and ensure that the relevant folders are included in the Send/Receive process, where applicable.
- Click OK to save any changes, then click Close to exit the Send/Receive Groups window.
- Select Send/Receive > Send/Receive All Folders to start a manual synchronization.
Wait for the operation to finish, then check whether new emails and other mailbox changes appear in the relevant folders.
Method 4: Update Outlook
|You can check and install the latest Microsoft Office updates to fix known bugs, improve Exchange connectivity, and restore normal Outlook functionality. Follow these steps:
Go to File > Office Account (or Account, depending on your Office version).
Select Update Options and then click Update Now.
Allow Office to download and install any available updates.
Once the update process is complete, restart Outlook and verify whether it is successfully synchronizing with the Exchange Server.
Method 5: Start Outlook in Safe Mode and Disable Faulty Add-ins
Outlook add-ins can sometimes interfere with application functionality. Starting Outlook in Safe Mode helps you determine whether an add-in is causing the synchronization problem.
Steps to start Outlook in Safe Mode
- Close Outlook.
- Press Windows + R to open the Run dialog box.
- Type outlook.exe /safe and press Enter:
- Select your Outlook profile if prompted.
- Check whether Outlook connects to Exchange and synchronizes the affected folders.
If synchronization works normally in Safe Mode, an add-in may be responsible.
Steps to disable add-ins:
- Open Outlook normally.
- Select File > Options > Add-ins.
- At the bottom of the window, locate Manage.
- Select COM Add-ins and select Go.
- Uncheck the enabled add-ins and select OK.
- Restart Outlook and check whether mailbox synchronization with the Exchange server works correctly.
- If Outlook synchronizes successfully after the add-ins are disabled, re-enable the add-ins one at a time and test synchronization after enabling each add-in. This helps identify the add-in that is causing the synchronization issue.
Method 6: Rebuild the OST File
If your OST file is corrupted, you may encounter issues like “OST file is not syncing”. In such a case, you can rebuild the OST file to resolve the issue. Since an OST file is only a local cached copy of your mailbox, Outlook can automatically create a new one by downloading fresh mailbox data from the server.
To rebuild the OST file, close Outlook and rename or move the existing OST file to another location. When you restart Outlook, it will create a new OST file automatically and begin synchronizing all mailbox items available on the Exchange Server. Depending on the mailbox size and network speed, the synchronization process may take some time to complete.
After synchronization finishes, verify that all your emails, contacts, calendars, and other mailbox items are available
Method 7: Use a Professional OST to PST Converter
If the OST file still fails to synchronize with the Exchange server after trying the above methods, the file may be damaged or inaccessible. In such cases, you can use Stellar Converter for OST to extract mailbox data from the original OST file. The software can scan inaccessible, orphaned, or damaged OST files, preview recoverable mailbox items, and convert them into PST format. You can then import the converted PST file into Outlook and regain access to emails, attachments, contacts, calendars, tasks, notes, and other mailbox data that may not be available on the server.
If you prefer not to install any software, you can use Stellar’s Online OST to PST Conversion Service. This web-based service allows you to upload your OST file & convert OST to PST without downloading a desktop application.
Conclusion
The Outlook OST file not syncing with the Exchange server issue can occur due to connectivity problems, incorrect Outlook settings, faulty add-ins, or a damaged OST file. You can fix this issue by checking Outlook’s connection status and synchronization settings. If the problem persists, try updating Outlook or rebuilding the OST file. If you need to recover mailbox data from an inaccessible or orphaned OST file, Stellar Converter for OST can help convert the available data into PST format for access in Outlook.