I tend to despise senders that believe email is always an effective real-time channel. Delays happen for all sorts of reasons, ranging from massive outages to scanning incoming emails for spam or malware (my corporate email is sloooow).
Greylisting has been so effective for my personal email, I don't mind waiting a bit on the rare occasion (by now, most senders are already recognized). And on the rare occasion I get spam, it's been cathartic, adding a rule to reject the sender with a quippy SMTP eerror. It's also been easy enough just to forward it to abuse@google.com, because it's almost always from Gmail.
Greylisting has been so effective for my personal email, I don't mind waiting a bit on the rare occasion (by now, most senders are already recognized). And on the rare occasion I get spam, it's been cathartic, adding a rule to reject the sender with a quippy SMTP eerror. It's also been easy enough just to forward it to abuse@google.com, because it's almost always from Gmail.