"Stale" SMTP sessions

[cfdynamics]

For the past couple weeks have seen a big increase in connections from China IPs that appear to be making a connection and not actually doing anything. They are just using up a session and hanging on for quite a while. Is there a setting somewhere that I am missing that would drop these connections after waiting a certain amount of time for a command to come through?

[twun]

I just created a windows firewall block, which blocks China, Russia and a few other top spamming countries. This really helped performance and unwanted spam.

[Brett Rowbotham]

I added a DNS blacklist for cn.countries.nerd.dk which is blocking quite a few Chinese connections.