BUMP!
I kind of got the same problem...
Followed the Wiki guide..
Improving Anti-spam system - ZimbraWiki
But I don't see any changes ...
When looking at the source for a email I don't see any pyzor/razor tags at all..
I'm pretty sure I did that before 4.5.x
When I followed this guide @ 4.0.x it worked perfectly and the spam was reduced
to just a few a week ,, now I get like 20-50 a day again.. (after upgrade)