Having only one IP I had to share the HTTPS port so depending on the request’s host either the Linux VM or Exchange 2007 should be queried. Unfortunately, although Exchange can be configured to process requests on another port Outlook and Pocket PCs will not work that way.
Therefore I’ve first set up Apache’s mod_proxy on the Linux VM to proxy Exchange – which did not and does not and will not work due to RPC over HTTPS, which Microsoft is said to have created standards incompliant. Apache’s developers refuse to implement an exception [the bug report], and versions of httpd newer than 2.0.53 won’t work, including my 2.2.8.
Unlucky me I did not recogize this only testing access to OWA. Hence my apologizes here to all affected.
ISA 2006 does not work with Windows Server 2008, and the new version requires too much overhead for my taste. BTW, it is referred to as ‘Stirling’ and a beta can be found here.
Finally, I’ve decided to give Squid a try. And, after reading just a few example configurations (and this) I managed to get it working. It proxies successfully to MS Exchange, and by letting Apache bind to 127.0.0.1 for SSL even the host-based (“vhost”) relay works. Here you can grab my configuration file squid.conf for proxying/relaying between Exchange and other hosts.
If you know what to change to access Exchange by SQUID without SSL please let me know. (Altering cache_peer line will let squid access only Apache and thus break host-based relaying.)