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Microsoft Outlook is one of the most widely used email clients that uses the OST file to work in offline mode. In the OST file, the mailbox data of the Exchange Server or Microsoft 365 account is continuously synchronizing. However, sometimes OST file synchronization issues in Outlook occur that affect the working flow.
These issues may cause emails, contacts, and calendars to stop updating properly. By checking connectivity, updating Outlook, repairing profiles, rebuilding the OST file, or using professional OST repair tools, users can effectively resolve synchronization problems and restore smooth Outlook performance.
In this guide, we will explain how to identify the issue, reasons, and the best ways to solve the error.
Recognizing OST File Synchronization Issue
Before diving into the solutions, first identify the error and then choose the appropriate fix based on the issue.
- The email you sent from Outlook doesn’t reflect in your webmail Sent folder.
- New emails you received on Webmail, but Outlook not receiving emails on your desktop.
- Calendar events you created are missing in the Outlook application.
- Error messages like “OST File is in Use and Cannot be Accessed” or “Outlook Data File Cannot be Opened” are shown.
- Duplicate emails appearing in your inbox.
- Outlook runs slowly or freezes when switching folders
If you are facing all these issues, then it is connected to the OST synchronization error.
Why do OST file Synchronization Issues in Outlook occur?
Understanding the reasons for the OST file sync error helps to create a roadmap to fix the issue. Here are some common causes.
- A corrupted OST file fails to open or sync certain folders or emails, contacts, and other items.
- If the OST file is too large, then it can affect the synchronization.
- For interrupted working, Outlook needs a stable connection with Exchange or Office 365.
- Sometimes, a severe side issue can cause the OST synchronization error.
- Using an outdated version of Outlook against an updated Exchange server can cause sync failures.
- Outlook stores account settings and configuration in a “profile.” If this profile becomes corrupted, then it affects synchronization even if the OST is healthy.
Methods to Fix Outlook OST File Synchronization Issues
Till now, we have known the reasons for the synchronization issue. Let’s find the solutions to fix the issue.
Method 1: Check Server and Internet Connectivity
Before we focus on complex methods, first try out the simple ones.
- Open a browser and verify you can access the internet.
- Try logging into Outlook Web Access (OWA) or office.com to confirm your account is accessible.
- Check if your organization’s IT team has posted a service alert.
- If you’re on VPN, try disconnecting and reconnecting.
If the server is down or your credentials have changed, fixing the OST file won’t help until connectivity is restored.
Method 2: Restart Outlook and Force a Manual Sync
Sometimes sync simply stalls and needs a push:
- Close Outlook completely from the task manager.
- Reopen Outlook and go to the Send/Receive tab.
- Click Send/Receive All Folders (or press F9).
- Watch the progress bar at the bottom of the screen.
If sync completes without any issue, the OST file synchronization issues in Outlook is likely a small glitch.
Method 3: Run the Inbox Repair Tool
If there is a minor issue with the Outlook data file, then using the built-in repair tool can repair the corrupted OST file(only in the new Outlook version). For that, first:
- Close Outlook
- Navigate to the Outlook installation folder. Common locations: C:\Program Files\Microsoft Office\root\Office16\
- Find the SCANPST.EXE file and run it.
- Click Browse and locate your OST file.
- Click Start to begin the scan.
- If errors are found, click Repair.
- Reopen Outlook and attempt to sync.
This tool handles structural corruption. It won’t recover permanently deleted items, but it can make a broken OST readable again.
Method 4: Delete and Recreate the OST File
If the repair tool doesn’t help, deleting the OST file forces Outlook to download a fresh copy from the server. You won’t lose any data since everything is on the server. However, this process can take a long time for large mailboxes.
- Close Outlook
- Go to C:\Users\[YourName]\AppData\Local\Microsoft\Outlook\
- Find the OST file associated with your account.
- Rename it instead of deleting the file. If something goes wrong, then you can recover your data.
- Reopen Outlook, and it will automatically create a new OST file and begin syncing from the server
Method 5: Create a New Outlook Profile
If your profile itself is corrupted, you need to start fresh:
- Close Outlook
- Open Control Panel → Mail → Show Profiles
- Click Add to create a new profile
- Follow the prompts to add your email account
- Set the new profile as the default
- Open Outlook and allow it to sync.
- If the data synchronizes swiftly, then the issue is with the older profile.
Method 6: Update Outlook
Go to File → Office Account → Update Options → Update Now. Allow any available updates to install, then restart and test sync. If a recent update caused the problem, check Microsoft’s known issues page for Outlook — a fix may already be available.
Use OST Recovery Tool for Advanced Repair Solutions
If the OST file synchronization issue in Outlook is still there and your OST file is corrupted, then using a professional OST recovery tool helps. BLR OST Recovery Tool is the secure approach to recover emails and other data from the corrupted OST file without any hassle. Try out the demo version of the software and experience it working.
Conclusion
OST file synchronization issues in Outlook are common, however it can be solved easily. Most of the sync issues are related to a corrupted OST file. In this post, we discuss the reasons and solutions to fix the issue. Try out the mentioned fixes and solve the Outlook OST file synchronization error.
