Hi Igor,
I've installed Plesk 9.5.2 a few days ago and the problem still exists how descripted above. This thread is nearly two month and your patch nearly one month old, now. Is there any reason, why Parallels didn't have released an update/hotfix yet? In my opinion greylisting is one of the main features in Plesk 9. When will plesk release an update via update manager? It's a pity, that I have to spend time to find a resolution for a solved problem.
Meanwhile please clearify, if your patch will work for Pleask 9.5.1 only or for Plesk 9.5.2, too.
Best regards
Martin