With my previous success with greylisting, I have decided that it definitely works well and is worth the little bit of effort it takes to get is installed.   Configuring postifx was very simple, and I (unfortunately) run several mail server that run Qmail.  After a few minutes of googling, I decided on qgreylist, which was the simplest implementation by far.
Several of the alternatives required patching and recompiling qmail, which I definitely didn’t want to do. qgreylist is just a simple Perl script that runs “in between” the tcpserver and the qmail-smtpd process.  You download it, change the path to it’s working directory, and tweak a couple other variables. Then copy it into a permanent location, and configure qmail’s smtpd process to send messages to it.  It took a little longer than postgrey, but not too bad.
there is another alternative that does not require patching and is written in C so it does not require to raise perl for each connection either. It has recently passed on freshmeat. Look at https://mij.oltrelinux.com/net/greylite/