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).
Email processing by amavisd was greatly reduced since the SMTP server rejected all new connections initially.
The “orange” is spam detected by amavis:
Below is the MariaDB database server.
Notice the drop in “pink” (ignore the spikes, those are backups) since the email server is rejecting before it has to query the database:
All things considered, SPAM and processing load has been greatly reduced.