Tobias Mueller commented:
As someone who runs an own email server, I have given up on greylisting (is there an appropriate alternative term that isn't referring to a colour? temporary banlist?), because it introduces a significant delay for email which can be quite annoying and, more importantly, it doesn't work well with the big players who tend to have many IPs, so I had to resort to manually allow-list quite a few networks. So I am curious whether you have some backup for your statement "greylisting [...] will be just as effective in blocking spam". Maybe I was just doing it wrong!