Information about the .ost (ost) file type

Below is all the information we have available on file about the .ost (ost) file type.

Microsoft Exchange Offline Storage file for e-mails (and folders). This allows emails to be viewed (and replied to etc) while disconnected from the Exchange server. The file contains a copy of the Exchange mailbox, thereby allowing offline viewing.

The default location used by Microsoft Outlook for .ost files is %UserProfile%\Local Settings\Application Data\Microsoft\Outlook, but this can be changed in the registry. The default name is outlook.ost.

If the file is deleted then Outlook will recreate the file automatically. This is true for Outlook 2003, but is not known whether this is true for other versions. Whilst Outlook will recreate the file, this can be a lengthy process because Outlook needs to pull down each of the folders and emails from the Exchange server.

The following link provides further information related to the .ost file extension:

Where this is available we would like to include file format information on .ost files, as well as information on how to view or open files of type .ost. If you know of any information which we have missed then please let us know.