why do I have two OST files with constantly the same exact size?

1. Rapid problem determination
Self-checking steps:
Open File Explorer → Enter the path:
%localappdata%\Microsoft\Outlook  
Check for the existence of two .ost files (e.g. Outlook1.ost and Outlook2.ost).
Compare the modification date and file size of the two files.
2. Common Causes
Possible scenarios:
Duplicate account configurations: the same mailbox account has been added multiple times
Possible scenario: Duplicate account configurations: The same mailbox account has been added multiple times.
Migration legacy: left over from the old version or when changing computers.
3. Security solutions
Method 1: Delete redundant OST files
Close Outlook (make sure the process exits completely)
Delete older or unused OST files (backup is recommended)
Restart Outlook, the system will automatically rebuild the cache.
Method 2: Rebuild the Outlook profile
Open Control Panel → Mail → Show Profiles
Delete the current profile → Create a new profile and re-add accounts
Method 3: Disable cache mode (temporary)
File → Account Settings → Double-click the mailbox account
Uncheck “Use cached Exchange mode”
Re-enable the feature after application
4. Preventive measures
 Avoid recurrence of the problem:
Regularly clean up the OST file (select “Outlook Cache” via Disk Cleanup utility)
Avoid logging in to the same account on multiple devices at the same time
5. Advanced check (optional)
Use the ScanPST utility:
Run SCANPST.EXE (path is usually C:\Program Files\Microsoft Office\root\Office16)
Scan and fix possible mailbox data errors