Outlook uses two types of files to store mailbox data on your local system. One is the OST file(offline storage table) other is the PST file(personal storage table). Ost file is used when you configure Outlook to work in offline mode. All offline work is being stored in OST file and gets synchronized with the Exchange Server when Internet connection resumes.
Some times while synchronization you may get the error message:
Unable to expand the folder. The set of folders could not be opened. Errors could have been detected in the file xxxx.ost. Quit all mail-enabled applications, and then use the Inbox Repair Tool.
Getting this error means your there is some issue with your OST file and it could not get properly synchronized with the Exchange Server. The reason behind OST file corruption may be one of the following:
- OST gets infected by a virus.
- Corruption of Exchange Server Database
- Exchange Server crash
- Deletion of mailbox from the Exchange Server
Resolution: As stated in the error message, quit all mail enabled applications that can use OST file.
- Find the OST file : A detailed explanation of where to find Outlook OST file
- Run the Inbox Repair tool (scanpst.exe) to repair the OST file.
- Recover the repaired items.
In some scenarios sacnpst.exe does not repair ost fie this is due to the fact that this tool does not works in complex cases of OST file corruption. If this method fails you should try third party ost recovery tool that convert ost to pst file. Such tools are capable of converting ost to pst file even in highest degree of OST file corruption and able to recover all components of .ost file such as emails, attachments, contacts, calander entries, notes tasks etc. Once you get the converted PST file you can save it to any disk or storage media and can open it directly with Outlook.