OST File - opening and understanding

Did your computer fail to open an OST file? We explain what they are used for and recommend software that we know can open or otherwise handle your .OST files.

What is an OST file?

An .OST file is an Outlook Exchange Offline Storage file. The Microsoft Outlook email application uses files that contain the .ost file extension. The OST files store email messages that have been saved from an exchange server by the Microsoft Outlook application.

The OST files that Outlook uses are created when a user chooses the "Use Offline Folders" option in the Outlook application. When this option is selected, the application stores the folders on the local hard drive instead of on the actual mail server that the application would usually download the files from. These files are then saved with the .ost file suffix.

OST files are similar in nature to PST files, but OST files allow for larger file sizes.

How to open OST files

You will need a program compatible with the specific file you are trying to open, as different programs may use files with file extension OST for different purposes.

While we have not verified the apps ourselves yet, our users have suggested 7 different OST openers which you will find listed below.

Suggest another file format using extension OST

While we know of one file format using the .OST file extension, there may be more. It is widespread that different programs use files with the same file extension for very different types of data. Please let us know if you are aware of a different kind of .OST file.

Various viewers for this file format

These apps are known to open certain types of OST files. Remember, different programs may use OST files for different purposes, so you may need to try out a few of them to be able to open your specific file.

SysTools OST RecoverySysTools OST RecoveryUser submitted
On-Screen TakeoffOn-Screen TakeoffUser submitted
PSTViewer ProPSTViewer ProUser submitted
CoolUtils Outlook ViewerCoolUtils Outlook ViewerUser submitted
PST WalkerPST WalkerUser submitted
PSTViewer LitePSTViewer LiteUser submitted
SysTools OST Viewer version SysTools OST ViewerSysTools OST Viewer version SysTools OST ViewerUser submitted
We have not verified any software that we know for certain will work with OST-files on Mac. If you know one, please use the 'Suggest a program' link below and tell us about it!
We have not verified any web services that we know for certain will work with OST-files. If you know one, please use the 'Suggest a program' link below and tell us about it!