Troubleshooting "HTTP 404" error messages in Outlook Web Access 5.5

If you use Microsoft Outlook Web Access (OWA), you may receive any of the following "HTTP 404" error messages: This article describes issues that may cause these error messages and how to resolve these issues.

These error messages may be caused by issues with any of the following features:

• DNS name resolution
• Proxy Server configuration
• Exchange virtual directory configuration
• Uniform Resource Locator (URL) creation
• The URLScan component of the Internet Information Server (IIS) Lockdown tool
• Port number assignment on the OWA Web site

The following sections describe how to resolve these issues.

DNS Name Resolution

The error messages that are described in the "Symptoms" section may occur if the computer on which you are running the Web browser is unable to resolve either of the following server names that you type in the Address box:

• http://servername/exchange
• http://fully_qualified_domain_name/exchange

If you cannot resolve the name of your server over the Internet, you may have to ask your Internet service provider (ISP) to create a DNS record for your server, which matches the fully qualified domain name (FQDN) that you want to use to access OWA.

If you cannot resolve the address on the internal network if you type the NetBIOS server name in the Address box, you must create a valid HOST record for this server on the DNS server that the client workstations are using for name resolution.

Alternately, you can add an entry for the OWA server to the HOSTS file on the workstation that is running the Web browser. For Microsoft Windows NT, Microsoft Windows 2000, and Microsoft Windows XP, this file is located in the X:\Winnt\System32\Drivers\Etc folder (where X is the drive on which the Windows folder is located). In Microsoft Windows 95, Microsoft Windows 98, Microsoft Windows 98 Second Edition, and Microsoft Windows Millennium Edition (Me), this file is located in the X:\Windows folder. This file is called "HOSTS" and it does not have a file extension (a sample file "HOSTS.SAM" may exist in the folder).

To add an entry for the OWA server to the HOSTS file on the workstation that is running the Web browser:

1. Start Microsoft Notepad, and then open the HOSTS file.
2. Use the following format to add an entry for the OWA server:
   ip_addressservername
3. Close and save file.
   
   Do not give the file a file name extension.
4. If you are using Windows 2000 or Windows XP, type the following command from a command prompt, and then press ENTER:
   ipconfig /flushdns

Proxy Server Configuration

You may receive an "HTTP 404" error message if OWA and Proxy Server are running on separate computers and you did not configure the Web Publishing feature of Proxy Server to forward requests to the OWA server.

To resolve this issue, enable Web Publishing to send requests to another Web server:

1. Start Internet Service Manager.
2. On the Action menu, click Web Proxy, and then click Properties.
3. Click the Publishing tab, and then click to select the Enable Web Publishing check box.
4. Click Sent to another web server.
5. Type either the internal IP address or the NetBIOS name of the OWA server.
   
   You can also use the FQDN as long as the name can be resolved by Proxy Server to the internal IP address.

For additional information about this issue or if more than one Web server exists, click the following article number to view the article in the Microsoft Knowledge Base:

Exchange Virtual Directory Configuration

You may receive an "HTTP 404" error message if the Exchange virtual directory folder is missing or if you renamed it under the Web site to which the users are connecting.

To resolve this issue:

1. Run the Exchange Setup program from the installation CD.
2. Use the Add/Remove option to see if the OWA entry has a check mark next to it.
   
   If the OWA entry has a check mark next to it, cancel Setup. If it does not, place a check mark in the box (leave the other options as they are), and then continue Setup. OWA is added to this server.
3. Start Internet Service Manager.
4. Expand the Web site in which you installed OWA.
   
   In a typical configuration, OWA is located under Default Web Site.
5. Verify that the Exchange virtual directory is listed under the Web site.
   
   If the Exchange virtual directory is listed under the Web site, go to step 3. If it is not listed, you must create an Exchange virtual directory.
6. Right-click Exchange Virtual Directory, and then click Properties.
7. Confirm that the local path is set to X:\Exchsrvr\Webdata (where X is the drive in which you installed Exchange 2000).
8. Make sure that the access permissions are set to Read-enabled.
9. Under the Application Settings section, confirm that the Permissions setting is set to Execute (including script).
10. Confirm the first of the three buttons that is listed in this section is labeled Remove instead of Create.
    
    If the first button is labeled Create, click this button to change the label to Remove.
11. Click the Documents tab, and then confirm that the Enable Default Document check box has been selected.
12. Confirm that "default.htm" and "default.asp" are listed in the documents list.
13. Click the Directory Security tab, click Edit in the Anonymous Access and Authentication Control section.
14. Confirm that the check box next to Allow Anonymous Access has been selected.
15. Configure either Basic Authentication or Windows NT Challenge/Response.
    
    To determine the authentication method that you want to use, find out whether the users will be accessing OWA from the Internet or through a proxy server or a firewall. If users access OWA through a proxy server or a firewall, use the Basic Authentication method.
16. Save and close the virtual directory properties.
17. Right-click Default Web Site, and then click Properties.
18. Click the ISAPI Filters tab.
19. Confirm that "exchfilt" is displayed in the ISAPI Filters list.
    
    If this filter is not listed, click Add, and then browse to the X:\Winnt\System32\Exchfilt.dll file (where X is the drive in which you installed Windows).
20. Click Save, and then click Close.

URL Creation

You may receive an "HTTP 404" error message if the URL address that OWA builds to open the message is incorrect. OWA calculates and checks the files in the Webdata folder to determine if the object is a file or folder. If you set flags such as "Archive" or "Compressed" on the folder, OWA may not calculate the folder correctly. In this situation, OWA produces the wrong URL.

To determine if you are experiencing this issue:

1. Reproduce the error message.
2. In the error message dialog box, point to Toolbars on the View menu, and then click Address Bar.
   
   If OWA creates an incorrect URL, the following URL is displayed in the address bar:

   javascript:parent.openNewWindow("/exchange/forms/IPM.NotefrmRoot.asp?...
   							

   The following URL is the correct URL:

   javascript:parent.openNewWindow("/exchange/forms/IPM/NotefrmRoot.asp?...
   						

This problem only occurs on servers that are running Exchange Server 5.5 Service Pack 1 (SP1). To resolve this problem, obtain the latest service pack for Exchange Server 5.5. For additional information, click the following article number to view the article in the Microsoft Knowledge Base: If you are experiencing this behavior on a later version of Exchange Server 5.5, the file that controls this process (Cdohtml.dll) may not be registered or it may be out of date. To resolve this issue:

1. Locate the Cdohtml.dll file on the hard disk.
   
   Typically, this file is in the X:\Exchsrvr\Bin folder.
2. Right-click the Cdohtml.dll file, and then click Properties.
3. Click the Version tab, and then view the Comments box.
   
   Confirm that the information in the Comments box describes the service pack level that you are currently running. If it does, go to step 4. If it does not, start the Services tool in Control Panel, stop the WWW Publishing Service, rename the existing Cdohtml.dll file to "cdohtml.old," and then copy the file from your latest service pack install point to the same folder.
4. From a command prompt, type the following command (where x is the drive in which you installed Exchange Server):
   regsvr32 x:\exchsrvr\bin\cdohtml.dll
   You receive the following message:
   DllRegisterServer in x:\exchsrvr\bin\cdohtml.dll Succeeded.
5. Start the WWW Publishing Service.

The URLScan Component of the IIS Lockdown Tool

If you are using OWA, you may not be able open messages that include certain characters in the subject line.

This issue can occur on a server that is running URLScan (which is a component of the IIS Lockdown tool). By default, URLScan blocks certain potentially harmful characters in the URL. The following list describes the blocked characters and the reason why they are blocked:

• Two periods (..): You cannot use folder traversals.
• A period and a backslash (./): You cannot use a trailing period on a folder.
• backslash (\): You cannot use backslashes in the URL.
• Colon (:): You cannot use alternate stream access.
• Percent sign (%): You cannot allow escaping after normalization.
• Ampersand (&): You cannot use multiple Common Gateway Interface (CGI) processes to run on a single request.

To resolve this issue, use one of the following methods:

• Describe this issue to users and explain that this issue limits OWA functionality even though it offers better security.
  
  -or-
• Edit the URLScan.ini file that is located in the X:\Winnt\System32\Inetsrv\Urlscan folder (where X is the drive in which you installed Windows) to allow these characters. If you do so, you allow potentially harmful commands to be used on the server that is running OWA, which may cause a security risk

For additional information about URLScan and Exchange Server, click the following article number to view the article in the Microsoft Knowledge Base:

Port Number Assignment on the OWA Web Site

The port number that the OWA Web site uses can cause this error. If the port number has been changed from the default port (80), users must specify the port number in the URL when they access OWA. For example, if the Web site is configured to use port 81, users must use http://servername/exchange:81 as the URL.