Summary: By default, Outlook set up an Exchange or Office 365 (Microsoft 365) profile in Cached Exchange Mode, which creates a folder called Sync Issues. It contains all the logs related to the synchronization of OST with the mailbox server. The Outlook synchronization log issues are generated when Outlook cannot synchronize the mail items from the OST file to the mailbox server. In this blog, we have discussed the reasons for the Outlook synchronization log issues and quick solutions to fix them without losing any mail items.
Outlook creates a local Offline Storage Table or OST file (also known as Offline Folder) when users add or configure their Exchange, Office 365 (Microsoft 365), IMAP, or Outlook.com account.
Any changes made by the user in their Outlook profile, such as drafting or deleting an email, are saved locally in the OST file and synchronized with the mailbox server later.
Similarly, updates on Outlook Web App (OWA), such as sending or receiving new emails, calendar or Shared mailbox folder updates, etc., are saved on the mailbox server and synchronized with the Outlook OST automatically.
This two-way synchronization keeps both—the local cache (.OST) and mailbox server—updated.
But sometimes, Exchange or Microsoft 365 (Office 365) users may encounter discrepancies between their Outlook client and Outlook Web App, such as outdated or missing messages and mail items.
This indicates Outlook synchronization issue, which can lead to severe problems such as,
Outlook synchronization issues and errors occur when Outlook cannot establish a secure connection with the mailbox or synchronize mail items due to poor connectivity, lack of permissions, or damaged OST files.
Although OST is a robust Outlook data file format, a large or oversized OST file is prone to damage due to integrity issues that can lead to synchronization issues.
Whenever Outlook fails to synchronize the mail items or folder stored in the OST file with the mailbox server, it generates a synchronization log stored in the Sync Issues folder. The folder contains three other synchronization issues subfolders,
However, the Sync Issues folder and its subfolders are not visible by default. To access the Synchronization Issues or Sync Issues folder, click on the three dots in the bottom left and choose ‘Folders.’
This brings up the Sync Issues and its subfolders containing all the synchronization logs.
If you see messages and mail items in the Sync Issues folder, open the Synchronization Log to check the issue. Then use the information provided in the message to troubleshoot the synchronization issues.
For instance, if you see the following error message in the Sync Issues folder with the subject ‘Synchronization Log:.’
Terminated in error [8004xxxxx-xxx-80040600-xxx] The client operation failed.
It indicates a damaged OST file.
IMPORTANT NOTE: Sync Issues may also arise when Outlook cannot synchronize certain mail folders, such as Junk Email (as shown in the screenshot above). The ‘Junk Email’ folder contains emails, which are not important and does not require any backup or synchronization as they may consume significant mailbox storage. Thus, administrators often set this policy to disallow synchronization of Junk Email and other non-important mail folders that can generate Outlook synchronization log issues. However, they can be ignored.
To resolve the Outlook synchronization log issues, check your network connection. Also, verify if the server is available and your profile is not deleted/disabled from the server.
For this, open the Outlook Web App (OWA) in a web browser and sign in using your account credentials. If you can access the account, follow these solutions to fix Outlook synchronization log issues.
Turning off cached Exchange mode will disable the Sync Issues folder and resolve Synchronization log issues. However, you need a reliable internet connection to enable and work in online mode. The steps are as follow,
This will disable the Cached Exchange Mode, and instead of synchronization, the Outlook will now connect and update directly on the Exchange or Office 365 server.
To create a new profile in Outlook 2007, Outlook 2010, Outlook 2013, Outlook 2016, Outlook 2019, or Outlook for Microsoft 365, follow these steps,
Rebuilding or recreating an OST file is a sure-shot solution to fix integrity issues and resolve synchronization log issues in Outlook 2019, 2016, 2013, and 2010. To rebuild a new OST file, follow these steps,
Wait for Outlook to finish synchronizing all mail items from the mailbox server and then check your emails and ‘Sync Issues’ folder for any Synchronization log issues.
If the OST rebuild fails or you find any missing emails or mail items from your profile after synchronization is done, convert the backup OST file to PST using an OST to PST converter tool, such as Stellar Converter for OST.
OST file rebuild often fails when the user profile is deleted or disabled from the Exchange Server or Microsoft 365. In such cases, you can use the software to move mailbox items from inaccessible or orphaned OST files to PST or directly export to an existing Outlook profile, Live Exchange Server, or Microsoft 365.
After the conversion, you can import the converted PST to your newly created OST file or any other Outlook account via the Outlook Import Export wizard.
For more help related to the Outlook synchronization log or other issues, leave a comment below or reach us via the Self Help and Support page.
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.
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