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 Outlook OST vs PST repair on the option of "File Name Extensions" to display extensions.

Repair Outlook Data Files (.pst and .ost)

This is all most people will need, searching for older items will be slower but for daily use items it will still be quick. As you close them, lead to the folder and right-click on the OST file. Once you re-open Outlook, your OST file is automatically recreated or rebuilt. If your hard drive goes through any physical damage, it will damage the data across it too. A bad sector or corrupted hard drive can cause OST inaccessibility.

Outlook - OST file recurring corruption

Although the repair process might recreate some of the folders, they may be empty. The FixTechGuide email error solutions Lost and Found folder contains any folders and items recovered by the repair tool that Outlook can't place in their original structure. You can use the Inbox Repair tool (SCANPST.EXE) to diagnose and repair errors in your Outlook data file.

• Open the OST file as per the location provided in the table.
• The Inbox Repair tool checks the Outlook data files on your computer to see if they're in good shape.
• 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 you said Outlook E3 licenses should support at least 100GB of data & there’s no excuse why it can’t support OSTs above 50GB when they offer twice that space.
• 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.
• We will help our readers decide the best way to rebuild OST for functioning through Outlook.
• You can use the Inbox Repair tool (SCANPST.EXE) to diagnose and repair errors in your Outlook data file.

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

When Outlook is running and is halted in such a way, it can damage the OST file. You might be working on something important across it when it happens. As you said Outlook E3 licenses should support at least 100GB of data & there’s no excuse why it can’t support OSTs above 50GB when they offer twice that space. In addition, you could open outlook in safe mode, maybe some add-ins affect the outlook. You could Right-click the Start button, and click Run, type Outlook.exe /safe, and click OK. Refer to this blog Solutions To Fix Error – "Errors Have Been Detected In The File Xxx.Ost" Solutions To Fix Error – "Errors Have Been Detected In The File Xxx.Ost" for the solution to this OST error.

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 flush DNS and re-sync Outlook 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.