Microsoft Exchange Server uses a specific type of service, which identifies all of the resources over the network and makes those resources accessible to Exchange Server users and related applications. This special service of Microsoft Exchange Server is called Directory Service. When a Microsoft Exchange Server crash takes place, the directory service gets impacted and you have to regenerate the service. In these situations, after you regenerate the Exchange Server Directory Service, Offline Storage (OST) file on the client system could not be synchronized with Microsoft Exchange Server user mailbox and so it could not be converted in PST (Personal Storage) file. Thus, you are required to manually Convert OST to PST using specialized applications...