[merrick33]

The Gmail issue you highlight I believe would only happen when the original outbound smtp server goes dark before it reattempts delivery. I say this because I have been receiving emails from Gmail with greylisting on for a week now.

[jrockway]

Look at the logs and you will notice a lot of initial attempts that are never "followed through" on, and these are from Google's IPs.

And BTW, spammers have figured out RFC822 now, so this doesn't even prevent a lot of spam.