Now a day, Maximum Windows user used Microsoft Outlook.

An OST file (.ost) is an offline folder file in Microsoft Outlook.

Offline folders make it possible for the user to work offline and then to synchronize changes with the Exchange server the next time they connect.

The ability to work offline is useful in environments with limited or unreliable connectivity.

Another type of file in Outlook is the PST file, which is simply stored on the client or a server other than the Exchange server.

Moreover, the user can get rid of such type of problem by using Outlook, File not will be access into Microsoft Outlook.