Half-Grey Listing

Concepts of http://nolisting.org and greylisting should be known.

Imagine this setup:
example.org         IN  MX  05 192.0.2.5
example.org         IN  MX  50 192.0.2.50
example.org         IN  MX  99 192.0.2.99

All addresses are on the same host running exim.
Exim would go through the whole process (almost)[0] as normal, but will tempreject (almost)[1] everything on 192.0.2.5 and 192.0.2.99.

Is anything wrong about this (WRT to RFCs)?
What might go wrong?


[0]: since most stuff is rejected anyway, one may want to optimize here
[1]: abuse@ and postmaster@ should probably be unfiltered, just to make sure