Outlook can use OST files to keep a local synchronized copy of mailbox information when an account is configured with Cached Exchange Mode. Depending on the Outlook setup, the file may contain locally synchronized emails, calendar items, contacts, and other mailbox data. An OST file is generally associated with an Outlook profile and its corresponding mailbox connection, while a PST file is commonly used for storing or transferring Outlook data. When an old profile or mailbox connection is no longer available, users may need to recover information that remains in a local data file. Before working with an Outlook data file, it is useful to identify the type of file, check whether the required folders and messages are available, and keep a backup copy of the original file. This can help protect the original data during recovery or export. Understanding how OST and PST files differ can make it easier to choose an appropriate method for accessing, preserving, or transferring Outlook mailbox information.