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Offline storage table (OST) files are offline files that store Outlook mail data and make it available to users when they are not connected to the Internet. The offline storage tables store mail data using the .ost extension. These files enable users to work with their offline inbox, offline outbox and make changes that are initially saved locally and are reflected in the server by synchronizing once the computer is connected to the Internet. Users can modify, add or delete the contents of these files just as a file located on the server can be modified.
Offline storage tables are the files that enable the offline mode of the Microsoft Outlook mail client. They are a type of database file that stores the data copied from the mail exchange server. The data copied include inbox emails, calendar and contacts. All such data and attributes are copied into the local OST files while the system is connected to the network and are stored in local storage under the local mail exchange server. The files are synchronized whenever the system connects to the mail server. Thus offline storage tables act as a cached exchange mode for Outlook.
Offline storage tables are similar to personal storage tables, but differ in the aspect that they can be used only with a Microsoft Exchange account or in a cached exchange mode.
OST files eliminate the need for multiple backup files and offer an easy way to access offline mail data. It is also easy to recover corrupted OST files with a simple OST-to-PST conversion. This is useful for recovering lost or deleted emails, images, attachments and other email attributes like from, to, subject, timestamp, CC , BCC and so on. They let users work with Outlook even during server downtimes and can support larger file sizes than PST files.
However, OST files require manual configuration and PST files can be responsible for both offline and online mail data. Hence, PST files are sometimes preferred over OST files. It is also not possible to open or back up OST files individually.