Offline Storage Table or OST file is the replica of user Exchange mailbox. It contains all the mailbox details and allows you to work offline when internet connection is not available or server is not connected. But what about the situation when user mailbox gets deleted from Exchange server making the emails and other Exchange mailbox data lost. There are various other issues that affect the OST file and make them inaccessible or unusable. The symptom of corruption may appear when you open Outlook, or work offline or check the emails stored in OST file. E.g. you start MS Outlook and get the following error message:
"Cannot open your default email folders. The file xxxx.ost is not an offline folder file."
Here, 'xxxx.ost' is name of the offline folder or the .ost file implicitly created by Outlook when it works with the Exchange mailbox offline. Since it is implicitly created, user does not get familiar with the files.
If your Exchange mailbox and email account are still valid after OST corruption, you can ensure that email account settings in Outlook are correct and Outlook is able to connect to Exchange server properly. You can start Outlook and send/receive your emails on the Exchange mailbox and Outlook will automatically create a new OST file and synchronize the data with the Exchange mailbox.
In case, the method does not work and you fail to get you OST data, you need to employ some effective software for repairing the unusable OST file. Commercial or third party software works the best at such situations and performs exact recovery of OST data which Outlook can synchronize with Exchange Server easily. To name a third party tool, OST to PST comes first as it seems to be the most appropriate solution for the users suffering from OST file corruption. Repairing OST file, recovering mailbox data and restoring them in new PST file are the major phases that this tool follows. Once OST is converted to PST, all data including emails, contacts, meetings, tasks and others become readable to the user.