While it's usually not necessary to relocate the offline cache used by an Exchange account, it is possible to move it to another folder or partition. For the most part, it only makes sense to move it if the C: drive is full.

Moving the offline cache so its easier to back it up is generally pointless: it's an offline copy of your Exchange mailbox and it can only be opened by the account that created it. If you try to use an old cache file, Outlook will complain that it doesn't match the server mailbox.

If the server fails and there is no server backup, the contents of the current, most up-to-date *.ost can be used to repopulate the server. In short, if you want a usable backup of your mailbox, export the contents to a *.pst file instead of including the *.ost in a backup file.

Move the *.ost in Outlook 2010 and older

In Outlook 2010 and older, you can move the ost used by cached Exchange to another location by disabling offline mode then changing the path on the Advanced tab of the Exchange account properties.

If you want to move the ost before you create a profile, use the ForceOSTPath registry value.

• Open Account Settings.
• Click More Settings (1).
• Deselect Use Cached mode (2) and click Apply.
• You can close Outlook and move the ost file now. If you want to create a new .ost file, you can skip this step.
• Click Outlook Data File button (3).
• Disable offline use (4) if Browse button is not enabled.
• Click Browse button to select moved ost file (5)

Using ForceOSTPath to set the file location

The ForceOSTPath key is supported by Outlook 2003 and up. In Outlook 2010, Outlook 2013 and Outlook 2016 it will apply to new accounts in a profile. In Outlook 2003 and 2007, it applies only to new profiles.

You need to set this key before you add the account to your profile.

Open the registry editor and browse to this key (create it if it doesn't exist). Create a string value named ForceOSTPath and add the path. (You can use variables if you are using group policy to push it out to your users.)

Outlook 2016

HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook

Expandable String Value: ForceOSTPath
Value data: full path you want to use.

Outlook 2013

HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook

Expandable String Value: ForceOSTPath
Value data: full path you want to use.

Outlook 2010

HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook

Expandable String Value: ForceOSTPath
Value data: full path you want to use.

Outlook 2007

HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook

Expandable String Value: ForceOSTPath
Value data: full path you want to use.

Outlook 2003

HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook

Expandable String Value: ForceOSTPath
Value data: full path you want to use.

Common variables

%APPDATA%: C:\Users\{username}\AppData\Roaming
%LOCALAPPDATA%: C:\Users\{username}\AppData\Local (Default for OST files)
%USERPROFILE%: C:\users\{username}
%WINDIR%: C:\Windows

Move the *.ost in Outlook 2013 or Outlook 2016

The method that worked in Outlook 2010 does not work with Outlook 2013 or Outlook 2016. When you try to change the location of the offline file (.ost) in Outlook 2013 or Outlook 2016, the Browse button is disabled.

There are two recommended methods to move the ost file: use the ForceOSTPath registry key or select the ost location when you add the account to the profile, both of which require you to remove and re-add the account to Outlook. (In Outlook 2003 or 2007, ForceOSTPath only works with new profiles.)

If you have an existing ost file, move the .ost file, remove and recreate the account in the profile using the Control panel, Mail applet and point it to the new location.

You could use Symbolic Links or Junction Points to repoint the folder where the .ost is stored. If you use this method you'll need to move everything in that folder to the new location.

The "not recommended" way to move the ost requires you to create a file to replace the ost. When Outlook chokes on it, you can then select the new location. You cannot reuse an old .ost file when you use this method, Outlook will need to create a new .ost file (it will cache locally, again, the whole mailbox from Exchange).

• Copy your .ost file to the new location. You can skip this step if you want to create a new .ost file.
• Open File, Account Settings or open the profile in Control panel, Mail.
• Remove the account from your profile.
• Click New.
• Enter your username and password and let Outlook find your account information.
• Select the Change account settings option, and then click Next.

• Click More Settings (1).
• On the Advanced tab, click Outlook Data File Settings. (2)
• Click Browse (3), browse to the .ost file that you copied in step 1, and then click Open.
• If you want to create a new .ost file, browse to the new location, enter a filename, and then click Open. Outlook will create the new .ost file.
• OK your way back to Outlook and then restart Outlook.

TIP: You can jump to the default .ost location in Windows XP, Vista, or Windows 7/8/8.1 by typing or pasting this command into the address bar of Windows Explorer and pressing Enter:

%USERPROFILE%\Local Settings\Application Data\Microsoft\Outlook