Re:Block email from Windows (Score 1)

Unfortunately a lot of businesses out there use exchange to send email...

But how many of them are running Exchange on Windows 98?

I agree that this may be a bit extreme for an ISP/business mail server, but I am doing this for my own personal domain. For a commercial server, you could use the fingerprinting to add a X-HostFingerprint header, and use that in your existing spam filtering to increase the spam score.

I'm still in the process of collecting statistics on this, before I flick the switch. But as I said, the only false positives I've seen so far are some Windows 2003 Server machines.

I will also be providing a method for servers to be whitelisted. The rejection will include a link to a page explaining the reason for rejection, and offering to whitelist legitimate servers by emailing postmaster.