To answer all your questions I have pinched a post by a Microsoft Support
Engineer (Rosa Yang), sorry its long but it excellently covers all your
questions:
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- A firewall or proxy server between the client computer and the server is
blocking requests from the browser on the client computer. For more
information, please see this KB article
Q296232 XCCC: Empty Inbox When Using Internet Explorer?5 and Later to Gain
Access to OWA
http://go.microsoft.com/fwlink/?LinkId=3052&ID=296232.
- The user¡¯s browser is not configured to allow Microsoft ActiveX controls
to run. Outlook Web Access?2000 with Internet Explorer?5 or later does not
require the user to download any new ActiveX controls, but it does take
advantage of existing controls.
To see if ActiveX controls are permitted to run in Internet Explorer:
a. In Internet Explorer, on the Tools menu, click Internet Options.
b. On the Security tab, click the zone to which your Exchange server
belongs, and then click Custom Level.
c. Under Settings, scroll down to Run ActiveX controls and plug-ins and
Script ActiveX controls marked safe for scripting, and then ensure that
these options are set to Enable.
If the above doesn't work then:
It is most likely that the WebDAV methods is not supported by the firewall.
Full Web-based Distributed Authoring and Versioning (WebDAV) support is
mandatory in order to access Exchange 2000 OWA through a proxy server or
firewall with Internet Explorer 5 or later.
To better understand this issue, we can take a look at the two versions of
OWA, the "rich" version, and the "reach" version. The one that you receive
depends on the Web browser that you use to access OWA. With Microsoft
Internet Explorer version 5.0 or later, you receive the rich client; with
all other browser versions, you receive the reach version. The server
determines the browser that the client is using from the User-Agent HTTP
header that the browser sends to the server with every request.
The rich client version of OWA takes advantage of the Microsoft XML control
on the client side and makes custom HTTP-DAV requests to the server by
using verbs such as SEARCH and PROPFIND. Some firewall and proxy servers do
not support these verbs and block requests, which results in the Web
browser failing to access OWA. The reach client is not affected because it
only uses standard HTTP verbs such as GET and POST.
Here are two workarounds for your reference:
- METHOD 1: Force OWA to treat Internet Explorer version 5.0 and later as
earlier versions. For additional information about how to force OWA to
treat Internet Explorer version 5.0 and later as earlier versions, please
refer to the following Microsoft Knowledge Base article:
Q296232 XCCC: Empty Inbox When Using Internet Explorer?5 and Later to Gain
Access to OWA
http://go.microsoft.com/fwlink/?LinkId=3052&ID=296232.
- METHOD 2: Use Secure Sockets Layer (SSL) on the OWA Web site to encrypt
the HTTP traffic so that the firewall cannot determine which HTTP verbs are
being sent.
The detailed steps are listed in this document:
320291.KB.EN-US XCCC: Turning On SSL for Exchange 2000 Server Outlook Web
Access
http://support.microsoft.com/default.aspx?scid=KB;EN-US;320291
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The only downside I have had with SSL is the initial authentication is
slooooow. Hope this helps