Offline folders or OST is the mirror image of the information stored on your e-mail server. It makes the data available even when you are disconnected with the network. The system creates one OST file per email profile. All the works that you perform offline are synchronized with the Exchange Server when Outlook gets connected with the network. The folders which are synchronized can be controlled using the Send/Receive settings. While working offline you can add, delete and modify the content of an OST file in the same way you do with a folder on server. One can change and move items in offline inbox, send messages to offline outbox and view offline public folders.
When you update the mailbox data of OST file to its corresponding server folder to make them identical, folders are synchronized actually and you can continue to work offline. Synchronization of folders is done by connecting to the server through dial-up networking which copies the changes made in each folder to the other folder and disconnect. If you delete any item from either the OST file or the corresponding server folder, it is deleted from both the locations after synchronization.
After you make changes in your email account profile, your current OST file may become unusable or you may face synchronization failure issue. Consider that you make a change in your email server name or mailbox name in MS Outlook. To synchronize the mailbox when you press F9 nothing is downloaded and an error message flashes on your screen.
The file .ost cannot be accessed because it has been configured for use with a different mailbox.
This kind of error message can appear in MS Outlook 2019,2016, 2013, 2010, 2007, 2003, 2002, 2000, 98 and 97. The issue happens when you try to synchronize your mailbox with an OST file that was used with a different email account of server. Further, you can fix the problem by changing the email account settings to their original state and copying the information from your mailbox to a personal folders or PST file. You can create new email profile with the new settings and include your old personal folder or PST file with the new email profile.
You need to ensure that the server and the OST file have the same information before you make changes to your email server settings. You can also copy the mailbox data and other information from the OST file to PST to use them later. When Outlook runs with the new email profile, copy the data from the PST file to your mailbox and synchronize it by pressing F9.
You can follow the above procedure when your OST file becomes unusable. But, sometimes, situations become cumbersome and some tricky solution is required to end up the issue. Hence, third party tools are developed that simply recovers the OST file and restores it. The OST to PST is a reliable commercial utility that governs appropriate solution to handle OST inaccessibility problem. With advance methodologies, it extracts OST data from unusable OST file, recovers them and saves in new PST file with utmost simplicity.