Outlook is using an old copy of your Outlook data file (.ost) fix

Introduction

Periodically, the Microsoft Outlook local data profile may become corrupt and give the following error when trying to start Outlook:

Outlook is using an old copy of Outlook data file (.ost).
Exit Outlook, delete the file, and restart Outlook.
A new file will be automatically created the next time you initiate a send/receive.

This can be quickly resolved by removing the old data file and letting Microsoft Outlook automatically redownload the data from the Exchange server.

How to resolve Outlook is using an old copy of your Outlook data file

1. Close Microsoft Outlook.

2. Navigate to %localappdata%\Microsoft\Outlook using File Explorer.

3. Delete the files with the extension .ost and .nst (If the file extension is .pst, copy it to another folder as these emails won’t be stored on the Exchange server and will be lost if the file is deleted. If you get an error saying the file is in use, use task manager to make sure Outlook.exe is not running.)

4. Re-open Microsoft Outlook.

Once Micrsoft Outlook is re-opened, the .ost and .nst files will be automatically recreated and the user’s emails will be redownloaded from the Exchange server.

Where is the Microsoft Outlook data file stored (.ost and .nst)

Windows 11 Outlook OST and NST location

C:\Users\%username%\AppData\Local\Microsoft\Outlook

Windows 10 Outlook OST and NST location

C:\Users\%username%\AppData\Local\Microsoft\Outlook

Windows 8 and 8.1 Outlook OST and NST location

C:\Users\%username%\AppData\Local\Microsoft\Outlook

Windows 7 Outlook OST and NST location

C:\Users\%username%\AppData\Local\Microsoft\Outlook

Windows Vista Outlook OST and NST location

C:\Users\%username%\AppData\Local\Microsoft\Outlook

Windows XP Outlook OST and NST location

C:\Documents and Settings\%username%\Local Settings\Application Data\Microsoft\Outlook