How to Open OST (Offline Data File) ?

This post will guide you to open a local client archive .ost file on your computer.

An OST is an offline folder file in Microsoft Outlook that is used with Microsoft Exchange Server. It is very helpful if you are using Outlook in an offline mode or if there are internet connectivity problems at your place. Working in an offline mode is, in fact, very similar to working with a mailbox on a server. The changes made in the offline mode are reflected when connection is restored and synchronization takes place. However, sometimes users need to access this OST file on a new machine/computer. Sometimes, these files can get corrupted due to various reasons and users want to open them anyhow.

Unfortunately, MS Outlook doesn’t provide any option to open an Offline Outlook Data File (OST) directly.  In these situations, when a user attempts to open/access OST file, the get some error messages like:

• The file you chose is not an Outlook Data File. You must select a new file of this type.
• Cannot open OST file. You must access Exchange at least once to use the OST file.

The above error messages appear each time when the users try to open an orphaned/corrupt OST file. To resolve the above problems and to open the OST file data, you will need to Convert OST to PST using a third-party application. Once, an OST file got converted to PST file, it can be easily imported into MS Outlook. Such third party tool employs advanced, yet safe mechanism to fix and convert OST file to PST. Once OST file is converted, the file can be opened in MS Outlook.