There may be items in the backup file that you might be able to recover that the Inbox Repair tool couldn't. Open the OST file as per the location provided in the table. As you open it across the File Explorer, lead to the "View" menu from the top. There, turn modern authentication troubleshooting on the option of "File Name Extensions" to display extensions.

Repair Outlook Data Files (.pst and .ost)

An Outlook data files are designed to safely handle max space 50GB in Outlook 2010 to 2019 and Office 365 by default. You can try syncing outlook file 6 to 12 months or through archiving email using retention policy, could be a better way to protect the .ost size from corrupt. As it is converted, you can easily view the contents of the data file.

Outlook - OST file recurring corruption

The functionality is diverse, and it can be approached in multiple directions. When the case comes to rebuilding the OST file, there are several things to look out for. If disable faulty add-ins in Outlook you can open the original Outlook Data File, you might be able to recover additional items. The Inbox Repair tool creates a backup file with the same name as the original, but with a .bak extension, and saves it in the same folder.

• Get your OST rebuilt properly with the help of the available techniques.
• Thus, you need to have a good anti-virus system to protect your computer.
• There may be items in the backup file that you might be able to recover that the Inbox Repair tool couldn't.
• There, lead into the "Data Files" tab and select your OST file.
• You could Right-click the Start button, and click Run, type Outlook.exe /safe, and click OK.
• Click the "Data Files" tab on the window and select your respective OST file.
• Click the "Open File Location" button to lead to the folder automatically.

What are the major Reasons of OST Corruption and how to Fix it

Fwiw, responding to my original post and how we addressed it for this user - we ended up creating new Outlook profile and limiting the amount of cached mail to 2 years. If the OST still gets corrupted when you have reduced the size there is something in the mailbox causing the problem. You must re-select "Account Settings" when it opens across a drop-down menu. There, lead into the "Data Files" tab and select your OST file. After selecting the file, click on "Open File Location" to redirect to the folder.

Method 4: Use OST Repair Tool

In certain cases, you must go for other methods to recover the data across OST files. If the respective file is not rebuilding from the above methods, there are other ways to get its data. This can be done with the help of PST files, another Outlook data file form. While they act as the basic backup data file for the user, the OST file troubleshoot Outlook synchronizing folders error can be easily converted to this form. Also, I forgot to mention that normally when the OST is corrupted you normally delete the file and recreate it.