Outlook OST and PST files can become corrupted for many reasons, the primary one being a forced or sudden shutdown of the program or system. If this happens, before beginning on the three stages to recover Outlook files, make sure that the system is repaired first, or the same thing will happen again. System failure most often results from a conflict or corruption originating in a 3rd party driver, firmware failure, or part of the Disk Subsystem failing. Once the system is stable, then you can go through the following three stages of Outlook recovery.
Stage 1 – Allow Outlook to Repair itself 
The first thing to try is to just start the program again. Outlook has a built in system that scans and repairs OST and PST files as they are loaded. This may be enough to repair any problem that exists. If the corrupted file is related to the email modules of Outlook, you can also activate the InBox Repair Tool. Microsoft, while not guaranteeing 100% stability in the product did have the foresight to include an option to allow you to restore Outlook from within the program. The InBox Repair Tool will only scan and repair the files associated with sent and received email, plus drafts.
Stage 2 – Use an Outlook Repair Program
If the repair tool native to Outlook cannot restore the file, it is time to move to using a data repair program. These are software packages with programs written based on experiential histories of common corruption repairs. This means that they will be able to repair and recover most of the files most of the time, but some files may not be able to be recovered. It is very important that before you use one of these programs that you are sure the system is stable, that your version of Outlook has all the current updates, and that the program you are going to use is both updated and is compatible with your version of Outlook. You can then run the program and set the parameters and controls according to the instructions to begin the Outlook repair.
Stage 3 – Use a Data Recovery Service
If there is still an OST or PST file that is corrupted and nothing else has worked, then it is time to contract with a data recovery service. These are repair professionals who will work with your files on an individual basis to repair and restore the information. It is best to use these services after you have used a program because it establishes a baseline for their approach as the program eliminates the most common repair options and they will not have to do those themselves.
Alan Chen is President and Chairman of DataNumen, Inc., leading in data recovery technologies worldwide. For more information on any of our products, including our Outlook repair programs, visit DataNumen.