I also actively block bad hosts but generally speaking the trend is down. I am happy. A major scalp for postscreen was dealing with amazon.com (my blog) and that is good and proves that there are problems with people who think Jeff Bezos is the answer to life the universe and the rest..
Postscreen in action is not exciting but permits or terminates the connection so that smtpd later on does not have to.
postscreen[x]: CONNECT from [22.214.171.124]:3953 to [?]:25 postscreen[x]: PREGREET 20 after 0.4 from [126.96.36.199]:3953: EHLO kgpigjmvi.com\r\n postscreen[x]: COMMAND TIME LIMIT from [188.8.131.52]:3953 postscreen[x]: DISCONNECT [184.108.40.206]:3953
It is not exciting but worth it