I will do that, and you should too. Nothing in the RCFs says emails are supposed to be instant. Reliable, yes. Instant, no. First, greylisting is HIGHLY eff

I will do that, and you should too. Nothing in the RCFs says emails are supposed to be instant. Reliable, yes. Instant, no. First, greylisting is HIGHLY effective. Something like 95% of email connections are spam. Almost all of them fail without ever hitting disk, via greylisting. If they actually retry, then the chance that the sender IP or email content is in an RBL is MUCH higher, so spam that actually retries will be more likely to be rejected at HELO by an RBL or filtered after it is accepted. The incidence of false positives with grey listing is VERY VERY low. Using greylisting means that very few emails need to be accepted and then filtered. Those are the false positives that really hurt. The sender receives no bounce, and the recipient probably doesn't look at his spam folder every day, especially when it is full of hundreds of junk emails. Greylisting makes email more reliable. In addition, better greylisting systems note senders that reliably retry and automatically whitelist them. My mail server actually delays less than 2% of legitimate emails due to greylisting.