Preliminary tests with ORF 4.1 and Windows Server 2008 are now finished with the following results:

ORF 4.1 + Exchange 2007 on Windows Server 2008 Standard (64-bit): SEEMS TO BE OK.
Installs fine, filters email. Requires more thorough testing to see if all features work.

ORF 4.1 + IIS SMTP on Windows Server 2008 Standard (32-bit): NOT COMPATIBLE.
The IIS ADSI provider seems to exist, but somehow it does not work. ORF will install fine with the above configuration, however it will not filter any emails, because the SMTP Module is unable to query the Pickup Folder path from the provider. Also, the ServerComment field, which is supposed to contain the SMTP Virtual Server name is empty. We may be able to work this around.

ORF 4.1 + IIS SMTP on Windows Server 2008 Standard (64-bit): NOT COMPATIBLE.
The Event.Manager Windows library is simply not registered for 32-bit. We use this (mostly undocumented) library to manage the SMTP event sink bindings. If the library binary is installed, like in the case of the Exchange 2007-ified CDOSYS, we may be able to work it around by registering the library. It is reasonable to assume that the same issues can be expected as in the case of the 32-bit version, it’s just ORF did not reach that point in testing.

ORF 4.1 + Exchange 2007 on Windows Server 2008 Standard (32-bit): NOT TESTED
As Microsoft strongly discourages using Exchange 2007 for production purposes, we do not plan to prepare any ORF versions for 32-bit Exchange 2007 usage.

Anyway, when you try to open the Current Sessions node in the IIS 6.0 SMTP Management MMC, you get an „Interface is not supported” error. It has nothing to do with ORF, it’s IIS. Anyone cares to submit this to Microsoft PSS? I understand that the SMTP Service is now considered obsolete and Exchange Edge Transport Servers are supposed to replace it, but… come on, this bug is quite hard to miss.