Create an Offline Folder file (.ost)

This feature requires you to be using a Microsoft Exchange Server e-mail account.

An Offline Folder file (.ost) is used to keep a local copy of your Exchange Server mailbox on your computer. The items in your .ost file are synchronized with the server when a connection is available.

On the File menu, click Work Offline.
Select or clear the Prompt me at startup so I may choose to work offline or online check box, and then click OK.
If you clear the check box, Outlook will automatically start offline if a connection to the server is not available.
Click Yes to copy the data from the server to your new Offline Folder file (.ost).

Note In Microsoft Office Outlook 2003, a new offline folder file format is introduced that offers greater storage capacity for items and folders and supports multilingual Unicode data. A file created in this format is not compatible with previous versions of Outlook and cannot be opened in a previous version of Outlook. Outlook automatically determines the format in which the offline folder file is created based on the version of the Microsoft Exchange Server, administrator settings, and formats of the data files that are configured for the profile. If the settings do not allow the file to be created in the new format, Outlook creates the file in the format that is compatible with previous versions of Outlook that does not support Unicode and offers the same storage capacity that was available in previous versions of Outlook.