What data file types does Outlook support? While working with Outlook, you will encounter two data file types: OST and PST. OST (Offline Storage Table) file types allow you to work offline.

Outlook Data File – The file C:\Users\<username>\AppData\Local\Microsoft\<username>\username.ost is in use and cannot be accessed. Close any application that is using this file, and then try again.

If you receive message Something is wrong with one of your data files and Outlook needs to close, when opening Outlook email client, see this post.

Your Outlook Data File is composed of a file header, located at the beginning of the document, and the actual data that makes up your personal folders. Contained in the header is information about ...

An Outlook Data File (.pst) file is a copy of the information in your Outlook account (including, but not limited to, emails, contacts, and appointments) stored on your local device.

Here is how to save and restore your Microsoft Outlook PST and OST files with Recovery Toolbox for Outlook.

The OST (Microsoft Exchange offline) file that is named as the email address you use with your Outlook account is the file containing contacts and other Outlook data.

When Outlook continually looks for data file errors, that's because Outlook believes there is a problem. However, to repair any errors, the data file -- more specifically the Outlook .pst file -- ...

What is a PST File? The PST File of Microsoft Outlook is a useful application that allows the storage of Outlook emails for both received and sent emails in the hard drive of the computer.

But when I try to open Outlook the next time, I get a pop-up that says this: “MS Office Outlook — The data file ‘Personal Folders’ was not closed properly.

Once you’ve installed Outlook onto the new PC, you’ll have a fresh, clean, and empty .pst file. You’ll have to import data from the old file to the new one.

What happens if your hard drive fails? Do you have a reliable backup of your Outlook data files? If not, I've got a tool you'll want to keep around just in case.