What you need to know about the OST (Offline Storage Table) file?
An OST (Offline Storage Table) file is a Microsoft Outlook data file that allows you to work with your mail, calendar, and other data items even without an internet connection. When you set up an Exchange or Office 365 account in Outlook, an OST file is created and encrypted with the MAPIEntryID GUID key.
When you access your mailbox in Outlook, the application associates your email account on the server with this key, facilitating the synchronization of emails and other data. However, if the Exchange server is unavailable or experiences a hardware failure, the OST file becomes orphaned, making it difficult to access your email data. Additionally, enabling the Microsoft Outlook Cached Exchange mode also creates an OST file.