This article was previously published under Q163589
Offline Folder files (OSTs) are considered slave replicas of the server- based folders. If you delete the master, the slave is orphaned.
If the original Microsoft Exchange profile was not modified, you can still start the Microsoft Exchange client offline with the old OST and recover the data by moving the messages from the OST to a PST file. However, if the old profile was deleted or modified (by using it to log onto a different mailbox) then the data in the OST is lost.
You can recover mail stored in an OST, provided that you have not tried to modify the profile that was used to create the OST file. If the profile used to create the OST file has been modified to point to a new mailbox, the information contained in the OST file may be lost.
This is because security on an OST works so that Windows NT authentication cannot be used when you work offline. Therefore, you must "prove" that you're allowed to log onto the server-based master before the OST file gives you local access. To do this, Exchange Server creates an encrypted "cookie" from your mailbox's unique entry ID while you are successfully logged into the Exchange Server computer. This cookie is securely stored in your Exchange Server profile. Essentially, your profile stores this key for the OST. Every time you try to access the OST file it checks your profile for the existence of this key.
If you modify the profile or try to connect to a new mailbox or new server with the current profile, Microsoft Exchange replaces this key with a new value from the mailbox that was created. At this point, you cannot access the data that was contained in the OST created against the first mailbox.
For more information, see the Microsoft Exchange Disaster Recovery Document on Microsoft TechNet or on the Internet at:
If you have not modified your profile or attempted to log on to the new mailbox, use the following steps to copy the offline messages to a PST:
Start the Exchange Client OFFLINE.
On the Tools menu, click Services.
Add a Personal Folders (PST) service.
Select the messages that you want to copy.
On the File menu, click Copy.
In the Copy to dialog box, select the personal folders (PST) that you created in step 4.
Repeat steps 5 through 8 for each folder that contains messages.
At this point, the messages are copied to a PST. You can create a new profile and you can log on to the new server-based mailbox. After you complete this successfully, you can add a Personal Folders service (by referencing the PST created above), and you can copy the messages from the PST back to the server-based mailbox.
NOTE: offline folders (OSTs) should not be considered as backups of your server based store. For more information on proper server backups, refer to the Microsoft Exchange Server Administrator's Guide, Chapter 15.