I've had the exact opposite experience. I've been using greylisting for almost a decade now. Greylisting is so common that people with broken mail servers is

I've had the exact opposite experience. I've been using greylisting for almost a decade now. Greylisting is so common that people with broken mail servers is a non-issue. It is literally just exchange 2003 without any updates applied. That is a tiny number of servers, and they will generate bounce messages when trying to deliver to tons of domains, not just yours. Greylisting cuts down on a huge amount of spam with virtually no additional load on your server like content filtering does. So, yeah, greylisting... good, good idea...