How to fix common OST synchronization issues in Outlook?

OST files are the backbone while you are working with outlook Email Client and Exchange server.  These files store all the user mailbox data and keep it synchronized with exchange database. If the connection to Exchange server isn’t available, then it provides users the capability to work offline. Whenever the Exchange connection is brought back its content and the changes made automatically gets synchronized with Exchange. 

While you are working in offline mode, you can compose and send emails. The sent mail is stored in the offline outbox, once the connection is reestablished the mail will be sent. The OST file data and the exchange server will get synchronized then, and the same changes will be reflected to both databases (i.e. the OST file and the Exchange EDB database). 

What will happen if the OST file isn’t able to get synchronized with the Exchange server?

The most common factor that leads to the Exchange to Exchange inavailability or an oversized OST file. 

In such situation either the Outlook starts troubling and prompting various error messages on the screen.
 

About OST file size:

The OST file location for various operating systems varies:
 

For Windows 95, 98 and ME:
C:\Windows\Application Data\Microsoft\Outlook
or
C:\Windows\Profiles\user name\Local Settings\Application Data\Microsoft\Outlook
 

For Windows NT, 2000, XP and 2003 server:
C:\Documents and Settings\user name\Local Settings\Application Data\Microsoft\Outlook
or
C:\Documents and Settings\user name\Application Data\Microsoft\Outlook

For Windows XP:
C:\Users\user name\AppData\Local\Microsoft\Outlook
Just like OST file location, the OST file size also varies for various Outlook versions.

Default maximum OST/PST file size limit for various Outlook versions:
Outlook 2002 and earlier versions             2 GB
Outlook 2003 and 2007                             20 GB
Outlook 2010                                             50 GB

As you keep on working with the OST file, it keeps growing in size day by day. You must keep a check on your OST file so that you can rescue it from getting oversized.
 

There are some symptoms that occur when your OST file size exceeds the limit. The user will not be able to open or load the OST file, Mail operations cannot be performed, no new data can be added to the OST file, and OST file couldn’t be properly synchronized with the Exchange server and various error messages are prompted on the screen indicating the failure of the OST to Exchange synchronization process.
 

At the beginning, the increasing OST file size can lead to troubles while performing daily mail operations such as composing, sending and receiving emails etc. But later on it can lead the user to serious data loss situations and major data corruption issues.

How to fix the OST synchronization issues?

To prevent the growing file size you can split the OST Files into smaller PST files. If the OST file data is inaccessible due to being oversized, you can use OST crop tool for breaking down the file into smaller chunks. If the OST to Exchange synchronization issues still persists then try Scanpst.exe and Scanost.exe utilities.Microsoft provides inbuilt repair tools for fixing the OST/PST related issues. You must try to fix your issues with them. If the inbuilt outlook repair tools don’t help you and your OST file data is still inaccessible, then you need some OST to PST converter. Using such tools you can safely convert the OST file into PST format. The converted PST file can be easily imported and accessed via Outlook.

Before that try out the following fixes to resolve the synchronization issues.

First ensure that your OST file is being getting properly synchronized or not.

Follow the given steps to check the OST Files are being synchronized or not?

• Go to the offline folder. Open its properties by right clicking.
• Go to synchronization tab here, you can view OST synchronization information Last Synchronized on: Date, Server folder contains: # Items, Offline folder contains: # Items.
• If the “# Items” value is different for Server folder and Offline folder that means the Offline folder and Server folder aren’t getting synchronized properly.

If synchronization has been done properly then you need to check the Outlook profile settings.

To do so follow the given steps:

For Outlook 2003

1. Go to Tools > E-mail Accounts. Under the email section, check the option View or change existing e-mail accounts checkbox is checked.
2. Click Next.
3. Go to Deliver new mail to the following location list and select the option Mailbox - account name
4. Select the option Microsoft Exchange Server and click Change.
5. Select the option Use Cached Exchange Mode and click Next.
6. Click Finish and then OK.
7. Restart Outlook.

For Outlook 2007

1. Go to Tools > Account Settings> Data Files tab
2. Ensure that the Mailbox - account name contains the default value.
3. Go to the E-mail tab> Mailbox - account name, and then click Settings.
4. Go to Advanced tab and Select the option Use Cached Exchange Mode then, click OK.
5. Close the Account Settings dialog box.
6. Restart Outlook.

For Outlook 2010

1. Go to File > Account Settings and then Select Account Settings.
2. Go to Data Files and Ensure that the Mailbox - account name contains the default value.
3. Go to the E-mail tab > Mailbox - account name. Select it and click Change.
4. Select the option Use Cached Exchange Mode then, click OK.
5. Close the Account Settings dialog box. Restart Outlook.

Once you have checked the above settings you are ready to perform the synchronization steps, which are given below.

Follow the given steps to manually synchronize the OST file with Exchange:

• Open the Folder List pane (or click Go > Folder List) and select your offline file folder from the list.
• Go to Tools> Send/Receive> Send/Receive All to synchronize all folders. You can also choose to synchronize only one folder by selecting ‘This Folder (Microsoft Exchange Server)’ option instead of selecting ‘Send/Receive All’

Follow the given steps to automatically synchronize the OST file with Exchange:

• Go to Tools> Options> Mail Setup.
• In the Mail Setup tab, go to the Send/Receive section. From there check the checkbox ‘Send immediately when connected’.
• Click Send/Receive to open the Send/Receive Groups dialog box
• Select the option Perform an automatic send/receive when exiting Click Close and then finally click OK to proceed further.

If it doesn’t help you to “rebuild the OST file” and let it get recreated and synchronized with Exchange.
 

Below given are the steps to create a new OST file:

Search for your OST file. If the default location isn’t known to you, you can go to start and then search for *.ost files in your system. 

• Rename the OST file extension (such as .old). 
• Go to file menu and close the open window.
• Start Outlook application.
• Go to Tools>Send/receive then click Send/Receive All.

It will automatically create a new OST file and synchronize it with Exchange.

If the above steps don’t fix your OST synchronization issue then there might be some error/damage in the Exchange Server support files. You can choose to remove the Exchange Server service support files automatically or manually do it by going to the "Fix it for me" section or "Let me fix it myself" section respectively.