When I implemented this, I ran into a nasty bug. Exchange, for some strange reason, looks up each email using the subject line (as opposed to say... THE FRIGGIN UNIQUE IDENTIFIER!). That means the email subject is part of the URL. If a percent symbol (%) is in the subject line of the requested email, Apache will complain that it cannot find the URL. This has to do with the way mod_proxy does encoding/decoding of URI escape sequences.

By using the following mod_rewrite rules and a simple bash script, one can easily work around this problem.

Insert this right before your "front-end" Proxy* directives in httpd.conf.

The simple bash script uses sed to work its magic. You'll notice I am also sending the original and changed URL to a log file in /tmp. This helps with troubleshooting and can be shut off when you're confidant everything is working. (This could easily be rewritten in any language.)

Keep in mind that this script only works if you implemented my solution exactly as I have. A man from Germany tried a modified solution, but could never get the percent rewrite to function properly. He used the ProxyPreserveHost directive, which I do not. By using this directive, you can dispense with the /etc/hosts hack and use the real OWA hostname in the ProxyPass directives (but not the ProxyPassReverse directives). I tried this and it works wonderfully... except for the percent symbol problem. I never could get the rewrite to work with the ProxyPreserveHost setup. I suspect this is due to my lack of understanding of the inner workings of both Apache's proxy subsystem and mod_rewrite.

Simon Blackstein returned and added an excellent comment about Outlook RPC over HTTP via Apache 2.0 proxying to this post (http://3cx.org/item/35). He says he still has a few minor issues, but I believe he'll work them out. Hopefully he'll report back here with any "fixes".

Here is his comment in full (with a few minor changes only to assist my HTMLization).

Simon wrote:

OK, so I'm still having a few funny issues with this config, as opposed to opening 80/443 directly to Exchange *shudder*.

BTW, this is very similar to proxying OWA really. A couple of other things involved. Like most people probably checking out this article, I only have a single Win2k3/Exch SP1 back-end server and an Apache reverse-proxy.

1. Check Q-article 833401 (http://support.microsoft.co...) to configure your Exchange server as a backend. Basically follow these instructions in the doc:-
   
1. Install the RPCProxy using 'Add/Remove Programs'. BTW, do make sure you reapply Win2k3 SP1 after installing this if you get the RTM version. This installs two virtual directories - /rpc and /rpcwithcert.
   
2. Configure correct permissions on the /rpc virtual directory (don't require SSL, you'll see why in a sec)
   
3. Hard-code the ports to communicate with the GC with the "ValidPorts" registry value using the Exchange server name
   
4. Hard-code proxy communications on all GCs by configuring the "NSPI interface protocol sequences" registry key
2. OK, before all of the testing stuff with Outlook, there is an important step they don't mention if you have a proxy. You want the proxy to terminate the SSL and communicate 80 back to the Exchange server, right? Well, you have to tell RPC to accept port 80 unencrypted traffic. Check the following article to see how that's done, they call it SSL offloading (whateva):
   
   http://www.microsoft.com/te...
   
   
3. Now, here's my httpd config to check out. You'll see stuff which I'm sure true Apache gurus will cringe at, but adapt to your own setup accordingly. Put your cert on the Apache box, obviously, and serve on 443. You'll find my OWA proxy settings and a nice redirect from 80 -> 443 in there too:
   
   
   <VirtualHost ***IP_that_you're_serving_on***:80>
   DocumentRoot "/var/www/proxy_dir"
   ServerName ***URL***
   Redirect / https://***URL***/exchange
   ErrorLog /var/www/proxy_dir/logs/error_log
   LogLevel emerg
   TransferLog /var/www/proxy_dir/logs/access_log
   </VirtualHost>
   
   <IfModule mod_ssl.c>
   SSLRandomSeed startup builtin
   SSLRandomSeed connect builtin
   
   <IfDefine SSL>
   Listen 443
   AddType application/x-x509-ca-cert .crt
   AddType application/x-pkcs7-crl .crl
   SSLPassPhraseDialog builtin
   SSLSessionCache dbm:/usr/local/apache/logs/ssl_scache
   SSLSessionCacheTimeout 300
   SSLMutex file:/usr/local/apache/logs/ssl_mutex
   
   <VirtualHost ***IP_that_you're_serving_on***:443>
   
   DocumentRoot "/usr/local/apache/htdocs"
   ServerName ***URL***:443
   ErrorLog /usr/local/apache/logs/error_log
   TransferLog /usr/local/apache/logs/access_log
   RequestHeader set Front-End-Https "On"
   SSLEngine on
   SSLCipherSuite ALL:!ADH:!EXPORT56:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP:+eNULL
   SSLCertificateFile /usr/local/apache/conf/ssl/server.crt
   SSLCertificateKeyFile /usr/local/apache/conf/ssl/server.key
   ProxyRequests off
   ProxyPreserveHost On
   <Location /exchange>
   ProxyPass http://***address_of_Exchange_server***/exchange
   ProxyPassReverse http://***address_of_Exchange_server***/exchange
   SSLRequireSSL
   </Location>
   <Location /exchweb>
   ProxyPass http://***address_of_Exchange_server***/exchweb
   ProxyPassReverse http://***address_of_Exchange_server***/exchweb
   SSLRequireSSL
   </Location>
   <Location /public>
   ProxyPass http://***address_of_Exchange_server***/public
   ProxyPassReverse http://***address_of_Exchange_server***/public
   SSLRequireSSL
   </Location>
   <Location /rpc>
   ProxyPass http://***address_of_Exchange_server***/rpc
   ProxyPassReverse http://***address_of_Exchange_server***/rpc
   SSLRequireSSL
   </Location>
   <Location />
   ProxyPass http://***address_of_Exchange_server***/
   ProxyPassReverse http://***address_of_Exchange_server***/
   SSLRequireSSL
   </Location>
   <Files ~ "\.(cgi|shtml|phtml|php3?)$">
   SSLOptions +StdEnvVars
   </Files>
   <Directory "/usr/local/apache/cgi-bin">
   SSLOptions +StdEnvVars
   </Directory>
   
   SetEnvIf User-Agent ".*MSIE.*" \
   nokeepalive ssl-unclean-shutdown \
   downgrade-1.0 force-response-1.0
   
   CustomLog /usr/local/apache/logs/ssl_request_log \
   "%t %h %{SSL_PROTOCOL}x %{SSL_CIPHER}x \"%r\" %b"
   
   </VirtualHost>
   </IfDefine>
   </IfModule>
   
   
4. Test it out! Run the Outlook /rpcdiag deal to get a nice interface to figure out what might be wrong, and check the Apache SSL logs for any funny errors. Oh, and make sure URLScan, if you have it installed, is not blocking anything it shouldn't.
   

Again, sometimes you do get some funny pauses happening, especially if you're on a shady connection. If anyone can find any way to make this more stable - I've been looking at the disable-cache thing potentially solving that - let me know.

Rgds,

Simon Blackstein