First, for the un-initiated, click here to learn about email greylisting.
When email admins talk about greylisting, one of the benefits they normally point to is load on the actual email server but fail to mention supporting systems. I did notice a decrease in mail processing load there as well as my database server.
Keep in mind this is NOT a busy email server. It’s only hosting a couple TLDs.
I noticed an immediate improvement after restarting mail services (I did not reboot the server).
All things considered, SPAM and processing load has been greatly reduced.