You would have undoubtedly heard about the Cached Exchange mode of Outlook and the incredible convenience that it offers to users of Exchange server, especially those who are constantly on the move. However, there are also many who use the Cached Exchange mode but find that they are unable to access their old Outlook data because of some problem with their mailbox. It is possible that the Exchange server administrator replaced the mailbox in order to correct some damage to the mailbox or perhaps even accidentally deleted it. If a mailbox has been deleted, the user may find it impossible to access the data in the offline folders - OST files. Of course, it is possible to turn to specialized tools to repair the orphaned files and recover exchange data. However, Outlook does provide an easier option through its Exchange Recovery mode.

As mentioned earlier, there can be many problems with the mailbox stored on a Microsoft Exchange server. A user who is using Outlook in a Cached Exchange mode has to protect the offline OST files but also be aware that the folders stored on the server mailbox may also become inaccessible. Either the mailbox may get deleted or software-hardware problems may make it difficult for the administrator to restore the mailbox to a previous state. Users believe that since they have a copy of the mailbox available on their local computers, in the form of OST files, their data too is safe. However, if the main mailbox on the server is deleted, the local OST files will not be able to work; in fact, they may become completely inaccessible and there may be no way to recover exchange data.

The reason why local OST files do not work if the mailbox on the server is deleted is that Outlook links each OST file with a specific Exchange mailbox by means of a key. When the mailbox on the server is deleted, the key to the mailbox is also lost, in some sense. When the user tries to access the data in the local OST files, the Exchange server has no way of knowing which mailbox the OST files are linked to and thus denies access to the user. If a new mailbox has been created, then Outlook will actually create a new OST file and you may lose all your data from the old OST files.

A much better option is to use the Exchange Recovery Mode in Outlook. When you use this mode, as soon as Outlook opens up with an existing Exchange server profile but finds that the corresponding mailbox does not exist or has been changed in some way, it immediately indicates so to the user. The user can then save all the old data in the OST file before creating a new profile so that the locally cached data can still be used to recover exchange information in some way. Using third-party tools such as Advanced Exchange Recovery from DataNumen, you can now restore data from the orphaned OST file, thus protecting the data associated with the old Exchange mailbox.