If a network interruption occurs during the synchronization process of Outlook, your OST files may become damaged or inaccessible, especially when data is being updated or when the connection drops. Damage to emails, contacts, and attachments may occur. To attempt to recover an OST file, I would recommend using OST recovery software. I have been using
Softaken OST Repair Software, which does recover OST file data and saves it into several formats, such as OST and EML. It is very easy to recover OST files while maintaining folder hierarchy and works with all Windows and MS Outlook editions.