Resolving OST Error: 'Unable to expand the folder

Published: 08th February 2010
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When Microsoft Outlook is used in conjunction with an Exchange Server account, it uses an offline folder, called .ost file, to store Outlook data. This file is an exact replica of your mailbox stored on Exchange computer and gives offline access. When Outlook comes online, the file synchronizes and connects with Exchange Server to download all the difference e-mails. However, there can be several situations when the OST file may get corrupted or orphaned. To access data in such situations, you either need a full data backup to restore or an OST Recovery utility to extract the valuable data.

To illustrate such problems, consider an instance when you try to open or synchronize an OST file in Outlook. You may fail in your attempts and receive the below error message:

"Unable to expand the folder. The set of folders could not be opened. Errors could have been detected in the file file_name.ost. Quit all mail-enabled applications, and then use the Inbox Repair Tool."

Where, 'file_name.ost' is the default OST file name that has been created by Outlook for use with Exchange Server.


The above error suggests that OST file is corrupt. However, few other reasons could be related to Outlook profile and account setting issues.


To solve the existing issue, you should consider these suggestions:

1)Make sure that the current e-mail account settings are correct and Outlook is properly connected to Exchange Server

2)Start Outlook again and click send/receive button to check if it can now synchronize the Exchange mailbox

3)Try creating a new Outlook profile and attaching the affected OST to it

If this doesn't help and your Outlook data remains inaccessible, you should use a OST to PST Recovery solution. These software are specifically built to scan a corrupted PST and convert it to a Outlook-usable PST.

The OST Recovery applications are scanning-based utilities built with an easy to operate user interface. You can install these software easily. The software are safe to use in all instance of OST inaccessibility issues since they use read-only algorithms.

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