Outlook Web Access

Adapt Functionality for Older Firewalls

Older firewalls that do not support DAV (Distributed Authoring and Versioning) extensions to the Hyper-Text Transfer Protocol (HTTP) may not allow WebDAV verbs. Because Internet Explorer 5 and later use WebDAV verbs in conjunction with Outlook Web Access, users will be unable to access their mailboxes with these browsers.

Because older browsers like Internet Explorer 4 or Netscape Navigator 4 do not use WebDAV verbs, they will not be affected by this problem.

If your organization uses a firewall that does not support WebDAV verbs, you will have to add the following registry key to allow Internet Explorer 5 and later users to access their mailboxes. Setting this registry key will force Internet Explorer 5 and later to render Outlook Web Access like older browsers. Therefore, Internet Explorer 5-only features, such as reminders, new mail notifications, and preview panes, will not be available to users.

Note   Another way to support Internet Explorer 5 and later with older firewalls is to use Secure Sockets Layer (SSL) encryption in all Outlook Web Access transmissions. Because SSL encrypts all HTTP traffic that passes through the firewall, older firewalls will not be able to filter WebDAV verbs. Be certain your organization can support SSL-only transmissions before trying this solution.

Warning    Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe. Note that you should back up the registry before you edit it, and you should also update your Emergency Repair Disk (ERD).

To adapt Outlook Web Access for older firewalls:

  1. On the Start menu, click Run, type Regedt32.exe, and then click OK.
  2. In Registry Editor, under HKEY_LOCAL_MACHINE on Local Machine, go to SYSTEM\CurrentControlSet\Services\MSExchangeWEB\OWA.
  3. On the Edit menu, select Add Value.
  4. In Add Value, type ForceClientsDownLevel as the value name, select REG_DWORD as the data type, and then click OK.
  5. In DWORD Editor, type 1 in the Data field . To disable this registry key and revert to normal Internet Explorer 5 behavior, type 0.