ARCHIVED: In Microsoft Outlook for Windows, what are offline folders, and how do I enable and disable them?

Note: Microsoft Outlook 2010, 2007 and 2003 offer Cached Exchange Mode in addition to offline folders. University Information Technology Services (UITS) at Indiana University recommends that you use Cached Exchange Mode instead of offline folders.

In Outlook 2002 or 2000, an offline folder file (ending with the extension .ost) is a file located on your computer's hard disk, by default in the C:\Windows directory. The contents are synchronized with the contents of your mailbox on the Microsoft Exchange server when you connect to the server. You can access offline folders even if the network or mail delivery service is down. You can also compact them to save space on your computer; see ARCHIVED: In Microsoft Outlook, what is AutoArchive, and how do I use it?

Using offline folders is a good idea if you want to synchronize your mailbox on a laptop or home computer so you can work when you are not connected to a network. Be careful when deleting folders, because if you delete a folder on the server or in the offline folders, that folder will be deleted on both the server and the local computer during the synchronization.

Note: When you create a new folder in Outlook, check the properties of that folder, using the steps below, to ensure that it is available offline.

Enabling offline folders in Outlook 2002

1. From the Tools menu, select E-mail Accounts....
2. Click View or change existing e-mail accounts, and then click Next.
3. In the "Outlook processes e-mail for these accounts in the following order:" list, click Microsoft Exchange Server.
4. Click Change..., and then click More Settings....
5. Select the Advanced tab, and then click Offline Folder File Settings....
6. In the "File:" field, type the path to the file you want to use as the offline folder file. The default filename is .ost. If this filename already exists, you will be prompted for a new name.

Enabling offline folders in Outlook 2000

1. From the Tools menu, select Options....
2. Select the Mail Services tab, and then check the Enable Offline Access box.
3. For each folder in your Folder List that you wish to synchronize with your Exchange mailbox, right-click the folder and select Properties....
4. Click the Synchronization tab. Under "This folder is available", select When offline or online. Click OK.

Disabling offline folders in Outlook 2002

1. From the Tools menu, select E-mail Accounts....
2. Click View or change existing e-mail accounts, and then click Next.
3. In the "Outlook processes e-mail for these accounts in the following order:" list, click Microsoft Exchange Server. Click Change..., and then click More Settings....
4. Select the Advanced tab. Click Offline Folder File Settings, and then click Disable Offline Use.

Disabling offline folders in Outlook 2000

1. From the Tools menu, select Services.
2. Select Microsoft Exchange Server, and then click Properties.
3. Select the Advanced tab. Click Offline Folder File Settings.
4. Click Disable Offline Use. Click OK three times.

Note: Deselecting the Enable Offline Use checkbox on the "Advanced" page will not remove the offline folder. You can remove the offline folder only by browsing to its location and deleting the .ost file.

You can get further information on offline folders from the Help menu in Outlook, and also from article 195796 at the Microsoft Help and Support web site.