Although, OST issues are quite severe when confronted but sometimes are simply caused by the careless shown at using them or associated applications that leads to such circumstances. If you are getting an error (cannot open your default email folders OST is not an offline) or complication while synchronizing Outlook OST data with Server then there is probably an issue behind it. But not all that is an error is a result of corruption, some even appear simply due to fault in the operations performed. OST to PST conversion is a good way to get out of such dilemma. It will provide complete access of OST file data after fixing all corruption and deletion issues.
It has been observed that plenty of times following a disaster that has taken place on Server; most Exchange Server Administrators are left with no other option that to rebuild entire Exchange Stores right from the scratch. Such a majorly risky step is usually taken by Server admins because of two prime reasons:
When the Exchange Stores are recreated from unexpected failures the users working with offline files i.e. OST get affected the most.
As part of the consequences, encryption passkeys of OST files that are kept in Exchange Information Store get replaced with a new one generated on the rebuild of Exchange Store. Thus, the users are rendered with OST data that is accessible but unreadable.
This situation makes Outlook unable to open OST file because of the loss of encryption passkey by getting replaced by a new one. Although, there are plenty of workarounds that can be implemented for come out of the situation but, there is no guarantee of it being completely infallible.
CAUTION: However, it is strictly advised to run an integrity check on the OST file before trying any of the lengthy workarounds suggested online. This is advised because the files there is a slight possibility of the OST file getting corrupted as part of the aftereffects.
If not due to this reason, corruption is possible of taking place in OST files making Outlook unable to open OST file. In case of corruption, users think that how to make OST file to PST format to read the information. They are strictly recommended to make use of third party solution for resolving the issue like cannot open your default email folders. The attempt to logon to Microsoft exchange has failed. For guaranteed results you can go for one such solution by the name of OST Converter tool that recovers as well as converts offline data to PST, MSG, and EML format respectively to renew it.
NOTE: Outlook cannot read ost file problem is generally surfaced by organizations still working on older versions of Exchange.