How to Fix Outlook and OWA Synchronization Issues

Outlook client and Outlook Web App (OWA) are two different modes to access Exchange or Microsoft 365 email accounts.

Outlook for Windows creates an Outlook data file, such as OST, to store a copy of mailbox items on the local machine. Offline Storage Table or OST (also known as Offline Folder) allows users to access their Outlook account and mail items even when the system is offline. The changes made in the Outlook client are first stored in the OST file and then synched with the Exchange or mailbox server based on the Outlook settings.

On the other hand, Outlook Web App or OWA runs on a compatible web browser, such as Google Chrome, and connects to the mailbox server directly. All the changes are made directly on the mailbox server, and thus, changes are updated in real time.

However, when the Outlook client fails to synchronize the changes stored in the Outlook data file or OST with the mailbox on the server, the changes are not reflected in the OWA. This can lead to discrepancies in the number of mail items or changes between Outlook client and Outlook Web App.

Besides, synchronization issues in Outlook can lead to problem in sending or receiving new emails, inaccessible or inoperable Outlook account, and outdated mail folders.

Reasons for Synchronization Issues between Outlook and Outlook Web App (OWA)

Synchronization issues between Outlook and Outlook Web App is a common problem that usually occurs due to damaged Outlook data files (.OST). However, it may also occur due to various other reasons such as,

• Faulty or incompatible Add-ins
• Poor network connection/firewall
• Corrupt Outlook profile/account
• Hardware or software issues

Symptoms of Synchronization issues Between Outlook and OWA

Following are the symptoms indicating synchronization issues between Outlook and OWA,

• Outlook frequently displays an error message when you synchronize OST file with the mailbox on Exchange Server
• Emails, notes, calendar items, or journal entries missing in OWA even after synchronizing OST via Outlook
• Mismatch in messages sent or received in Outlook client and OWA
• Outlook displaying new issues in Sync Issues folder

Solutions to Fix Outlook and OWA Synchronization Issues

Follow these solutions to troubleshoot and fix synchronization issues between the Outlook client and OWA.

Solution 1: Check Network Connection

An unreliable or poor network connection can prevent Outlook clients from synchronizing the OST file to the mailbox on Exchange or Microsoft 365 Server. Reconnect the Ethernet cable or Wi-Fi and verify Exchange Server is online and you can access the internet. Also, check your firewall settings to prevent Outlook clients from connecting to the server and synchronizing the OST file with the mailbox server.

Solution 2: Check Sync Issues

The Sync Issues folder contains the synchronization logs that can help you troubleshoot the synchronization issues between Outlook and Outlook Web App (OWA).

However, Sync Issues and its subfolders are not visible by default. To view these folders,

• Click the three dots at the bottom navigation pane and choose ‘Folders.’

This will display the Sync Issues folder and its three subfolders.

• Local Failures

Contains mail items that could not be sent to the mailbox server from the local Outlook data file, i.e., OST.

• Conflicts

Contains multiple copies of conflicting mail items in the mailbox.  

• Server Failures

Contains mail items that could not be synchronized with the mailbox server. If you can’t see mail items in OWA, check this folder in the Outlook client.

Delete the mail items from Sync Issues and its subfolders and restart Outlook. Wait for the auto-synchronization to start. If you still see new logs or mail items in Sync Issues or its subfolders, follow the next solutions to fix the synchronization issue.

Solution 3: Manually Synchronize the OST and Exchange Server Mailbox

You may start manual sync by pressing the F9 key while Outlook is open. The changes in the OST file will be synced with the mailbox on the Exchange or Microsoft 365 server.

You may also click the ‘Update Folder’ option under the ‘Send/Receive’ tab to manually synchronize the changes stored locally in the OST file to the mailbox server. After successful synchronization, OWA should reflect the changes and updates.

If this works, check enable the auto-sync setting to fix this issue permanently.

Solution 4: Enable Auto Sync

The steps to enable auto-synchronization between Outlook and OWA are as follow,

• In Outlook 2013, 2016 or 2019, navigate to File>Options>Advanced.
• In Outlook 2010, go to Tools>Options>Mail.
• Click the ‘Send immediately when connected’ checkbox under the ‘Send and receive’ section.

• Then click the ‘Send/Receive button and enable the ‘Perform an automatic send/receive when exiting’ option.

• Click ‘Close>OK’ and then restart Outlook.

Solution 5: Repair Outlook Data File (OST)

You can use the Inbox Repair Tool or SCANPST.EXE to repair the OST file errors that might fix Outlook and OWA synchronization issues. The steps are as follow,

• Run SCANPST.EXE. It’s located in the Microsoft Office installation directory. Refer to this guide to find the SCANPST.EXE.
• Click ‘Browse’ and choose the OST file. Follow this guide to find the OST file location.
• After selecting the OST file, click ‘Start’.
• If errors are found, click the ‘Repair’ button to fix OST file errors. The Inbox Repair Tool creates a backup of your OST file and then repairs the original OST file.

• After the repair, open Outlook and check if the synchronization issue is fixed.

Solution 6: Rebuild Outlook Data File (OST)

If the manual or auto sync fails to fix the synchronization issues between Outlook and OWA, it indicates a problem with the Outlook data file (OST). To fix this, you can rebuild a new OST file. The steps are as follow,

• In Outlook 2013, 2016, or 2019, navigate to File>Account Settings>Account Settings.
• Click on the ‘Data File’ tab and select the email account.
• Click ‘Open file location…’ and then close the Outlook client.
• Move the OST file to a safe location. You may also delete the OST after taking the backup.  
• Restart Outlook. A new OST file will rebuild automatically.

Outlook will start the synchronization process and download the mail items from the mailbox on the Exchange Server to this newly created OST file. This should fix the problem.

However, if there are missing items in your mailbox or Outlook, convert the backup OST file to PST using Stellar Converter for OST and then import the converted PST to your new OST file via Outlook Import Export wizard.

The tool also comes in handy when OST file rebuild fails due to the disabled or deleted mailbox from the Exchange Server or Microsoft 365. The software can also help you move mailbox items from an inaccessible or orphaned OST file directly to Live Exchange Server or Microsoft 365.

Read More: How to import OST to Office 365

Conclusion

Synchronization issues between Outlook and OWA can cause mismatches and discrepancies in the mail items. When Outlook fails to synchronize the mail items from the local Outlook cache (OST), it may display send/receive errors that prevent users from sending or receiving new mail items. In this blog, we discussed various solutions that you may apply to fix the synchronization issue between OWA and Outlook clients.

For more help related to Outlook or Outlook data files, such as OST to PST, leave a comment or reach us via the Self Help and Support page.

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About The Author

Ravi Singh

Ravi Singh is a Senior Writer at Stellar®. He is an expert Tech Explainer, IoT enthusiast, and a passionate nerd with over 7 years of experience in technical writing. He writes about Microsoft Exchange, Microsoft 365, Email Migration, Linux, Windows, Mac, DIY Tech, and Smart Home. Ravi spends most of his weekends working with IoT (DIY Smart Home) devices and playing Overwatch. He is also a solo traveler who loves hiking and exploring new trails.