How to Fix OST File Synchronization Error – Free Guide

Updated On - October 25, 2023 by Henry Bray | Reading Time: 4 minutes

The OST file as the root of your Outlook that helps to store and synchronize all data with the Exchange database. If there is no way to connect to the Exchange server, the OST file can be used offline. The OST file syncs automatically, so all your offline tasks will update once they are properly connected to the Exchange server. In this blog, we explain manual ways to fix OST file Synchronization error. Lets start.

However, it has been seen many times that when you open your MS Outlook or try to sync with your Exchange mailbox, you are prevented from doing so and hence you face various OST sync error messages. , Which appear in the sync log in the Deleted Items folder. Such synchronization issues occur when one or more corrupt or damaged email messages are found in the OST folder, which cannot be fixed during the synchronization process. Here in this blog, we explain all the common synchronization issues of OST and find solutions to fix OST file synchronization error.

Related Blog: How to Extract Contacts from Outlook OST file

Why Exchange OST File Synchronization Error Occurs?

However, not very often, but you may face many synchronization errors when you connect OST to the Exchange mailbox. Outlook 2003, 2007, 2010, 2013, 2016 and 2019 have different reasons for preventing synchronization with Exchange.

  • The network connection may be the main cause of the synchronization issue.
  • MS Exchange Server also fails more frequently, due to which Outlook cannot be synchronized.
  • Problems on the local computer are another common problem when Outlook malfunctions.
  • Sudden system shutdown, oversized OST files, and virus attacks are some of the most common reasons.

3 Verified Methods to Fix OST file Synchronization error

The OST of the Outlook email application is only synchronized with the Exchange Server mailbox when there is a connection to Exchange Server. The synchronized speed varies depending on the data size and Outlook version. Here we have explained different steps to solve the OST synchronization issues, such as verifying user profile, cached exchange mode etc. you can follow the mentioned steps to get rid of these issues.

Step 1 – Verify Synchronization of OST files

You can follow these steps to check the synchronization of Offline Storage files with proper attention –

  • Right Click on the folder you want to check and click “Properties”
  • Switch to the “Synchronization” tab. If you don’t see the Sync tab, you haven’t set up your profile to use offline folders.
  • Select “Statistics” of this folder and check these attributes –
    • Server folder contains – Items
    • Last synchronized on – Date
    • Offline folder contains – items

If you did not experience any problems with OST synchronization, then the attribute value of the folder of the Server as well as offline folder contents are the same. But, if you cannot find these values the same, then there must be a conflict synchronizing both databases. In that case, you have to follow these processes to verify profile settings.

In Outlook 2010

  •  Go to the “File” menu and click “Account Settings”.
  • Now, choose “Account Settings” from the list.
  • Click the “Data Files” tab and set “mailbox account name” as default.
  • Click the Email tab, click “Mailbox – account name”, and then “change”.
  • Make sure that “Use Cached Exchange Mode” is selected, and click “OK”.
  • In the “Account Settings”, click “Close”.
  • Quit “Outlook “and reopen it again

#In Outlook 2007

  • Click on “Tools” then “Account Settings.”
  • Click “Data File” and set “Mailbox account name as default.”
  • In the Email tab, go to “Mailbox – account name” and Settings.
  • Check the option “Use cached Exchange Mode” and click OK.

In Outlook 2003

  • The Tools menu, click “Email Account”.
  • Email section, select “View or change existing email accounts” and click “Next”.
  • In the “Deliver new email to the following location” list, select “Mailbox – Account name”.
  • Click the “Microsoft Exchange Server” object, and click “Change”.
  • Select “Use Cached Exchange Mode”, and click “Next”.
  • Click the “Finish” button.
  • Close the Outlook and restart Outlook again

Step 2 – OST File Synchronization

Now you can easily perform these two important methods to synchronize your Offline folder – Manual and Automatic methods to fix OST file synchronization issues accurately.

For Manual Synchronization

This process will help you to synchronize offline folders for Outlook 2019, 2016, 2013, 2010.

  • Go to the “Folder List” pane, choose the Folder which you want to synchronize.
  • Go to the “Tools” menu, click “Send/Receive”, then Microsoft Exchange Server, if you have a specific folder
  • In Tools menu, go to “Send/Receive All” for all folders

As soon as the synchronization process starts, you will see a synchronization status message on your computer screen. If there are too many items found in your mailbox and your offline folders have not been synchronized for some time, then, in this case, the synchronization process can take longer than 30-40 minutes.

For Automatic Synchronization

You can use this method to synchronize the OST file with Exchange Server anytime you go online.

  • Choose “Tools” and “Options”
  • In Mail Setup, select “Send Immediately when connected.”
  • In Send/Receive, select “Send/Receive groups” and check “Perform automatic send/receive when exiting”.
  • Then click “close”.

Step 3 – Create New OST File and Synchronize

If you cannot fix the synchronization issue even after using the above methods and fail to synchronize it, your OST file can be corrupt or damaged. In that case, you have to recreate OST file and then re-synchronize it again.

How to Rebuild New OST?

  • Close Outlook email application.
  • Go to C:\Users\administrator\AppData\Local\Microsoft Outlook
  • Find the OST file and rename the old file with a different extension. (For example, replace .OST with .OLD extension).
  • After renaming the file, a new file will be created
  • In Outlook, go to “Tools” and “Send/Receive.”

Related Article: How to Access OST file in Thunderbird


If you still can’t solve the OST synchronization issue, you can try the scanost.exe or scanpst.exe tool developed by Microsoft. These are the default repair tools created by Microsoft to fix OST and PST files related issues. But if these tools also do not work, in this case, you can take the help of Regain OST Converter tool that can efficiently solve all the problems related to OST files. If you have an oversized OST file and this tool also helps you in that case as well.

Free Download100% Secure Buy NowPrice: $39

Regain OST to PST Converter is a very reliable and professional tool as it can easily repair OST files that are severely corrupt or damaged, which default repair tools cannot fix. If the above methods are no longer helpful, use this tool to resolve OST problems and recover them with a few easy steps.

Author: Henry Bray

Henry Bray is a young technologist and content a Content Writer at Regain Software, loves to write about MS Outlook, MS Exchange Server, Office 365, Mozilla Thunderbird and many more email applications.

3 thoughts on “How to Fix OST File Synchronization Error – Free Guide”

  1. Avatar Elijah Gann says:

    Your instructions are easy to follow, and the visuals make it even easier to understand. It provided many useful tips and some helpful links as well. I highly recommend it for anyone who is having trouble with their Outlook setup!

  2. Avatar Doris says:

    This is an informative blog post that outlines an effective approach to fixing OST file synchronization errors. It clearly explains the steps involved and provides helpful tips for troubleshooting. It is also a great resource for anyone who is dealing with this issue.

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