An OST (Offline Storage Table) file is automatically created by Microsoft Outlook when you configure an Exchange, Microsoft 365, or another supported account for offline synchronization. It allows Outlook to maintain a local copy of mailbox data, including emails, contacts, calendars, tasks, and other items, so you can access synchronized information even when an internet connection is temporarily unavailable. To create an OST file, first install and open Microsoft Outlook. Select File > Add Account and enter your Exchange or Microsoft 365 email address. Follow the on-screen instructions to complete the account setup and provide your password if required. After authentication, Outlook begins synchronizing the mailbox with the local computer. During this process, Outlook automatically creates an OST file in the configured Windows user profile. You generally do not need to manually create an OST file or choose its format. Outlook manages the file automatically according to the account and profile configuration. The location of the OST file can usually be found under the user's Outlook data directory. If you create a new Outlook profile and configure a supported Exchange or Microsoft 365 account, Outlook will normally generate a new OST file for that profile. If an OST file becomes corrupted or inaccessible, Outlook may stop synchronizing mailbox data. In such situations, users can consider repairing the Outlook profile or using specialized OST recovery software to extract accessible mailbox items and save OST Data in PST or other formats.