I have updated my mail server code to report some very basic diagnostics data through performance counters (I'll come back to that in a future post). Amongst the information that's being logged are:
- The total number of connections since the server was started.
- The total number of connections refused (due to server and anti-spam policies) since the server was started.
I've looked at these numbers after a couple of hours of the server being online. There were about 60K connections, out of which a bit more than 75% have been refused SMTP transactions because the remote hosts were identified as spam senders.